diff --git a/modules/appnexusBidAdapter.js b/modules/appnexusBidAdapter.js
index d46be776b59..7db2b9aab2f 100644
--- a/modules/appnexusBidAdapter.js
+++ b/modules/appnexusBidAdapter.js
@@ -216,20 +216,24 @@ function newBid(serverBid, rtbBid) {
       body: nativeAd.desc,
       cta: nativeAd.ctatext,
       sponsoredBy: nativeAd.sponsored,
-      image: {
-        url: nativeAd.main_img && nativeAd.main_img.url,
-        height: nativeAd.main_img && nativeAd.main_img.height,
-        width: nativeAd.main_img && nativeAd.main_img.width,
-      },
-      icon: {
-        url: nativeAd.icon && nativeAd.icon.url,
-        height: nativeAd.icon && nativeAd.icon.height,
-        width: nativeAd.icon && nativeAd.icon.width,
-      },
       clickUrl: nativeAd.link.url,
       clickTrackers: nativeAd.link.click_trackers,
       impressionTrackers: nativeAd.impression_trackers,
     };
+    if (nativeAd.main_img) {
+      bid['native'].image = {
+        url: nativeAd.main_img.url,
+        height: nativeAd.main_img.height,
+        width: nativeAd.main_img.width,
+      };
+    }
+    if (nativeAd.icon) {
+      bid['native'].icon = {
+        url: nativeAd.icon.url,
+        height: nativeAd.icon.height,
+        width: nativeAd.icon.width,
+      };
+    }
   } else {
     Object.assign(bid, {
       width: rtbBid.rtb.banner.width,
diff --git a/src/adaptermanager.js b/src/adaptermanager.js
index 670b329ef72..12a15f7c3c8 100644
--- a/src/adaptermanager.js
+++ b/src/adaptermanager.js
@@ -149,6 +149,9 @@ function getAdUnitCopyForClientAdapters(adUnits) {
 
 exports.makeBidRequests = function(adUnits, auctionStart, auctionId, cbTimeout, labels) {
   let bidRequests = [];
+
+  adUnits = exports.checkBidRequestSizes(adUnits);
+
   let bidderCodes = getBidderCodes(adUnits);
   if (config.getConfig('bidderSequence') === RANDOM) {
     bidderCodes = shuffle(bidderCodes);
@@ -211,6 +214,54 @@ exports.makeBidRequests = function(adUnits, auctionStart, auctionId, cbTimeout,
   return bidRequests;
 };
 
+exports.checkBidRequestSizes = (adUnits) => {
+  Array.prototype.forEach.call(adUnits, adUnit => {
+    if (adUnit.sizes) {
+      utils.logWarn('Usage of adUnits.sizes will eventually be deprecated.  Please define size dimensions within the corresponding area of the mediaTypes.<object> (eg mediaTypes.banner.sizes).');
+    }
+
+    const mediaTypes = adUnit.mediaTypes;
+    if (mediaTypes && mediaTypes.banner) {
+      const banner = mediaTypes.banner;
+      if (banner.sizes) {
+        adUnit.sizes = banner.sizes;
+      } else {
+        utils.logError('Detected a mediaTypes.banner object did not include sizes.  This is a required field for the mediaTypes.banner object.  Removing invalid mediaTypes.banner object from request.');
+        delete adUnit.mediaTypes.banner;
+      }
+    }
+
+    if (mediaTypes && mediaTypes.video) {
+      const video = mediaTypes.video;
+      if (video.playerSize) {
+        if (Array.isArray(video.playerSize) && video.playerSize.length === 2 && Number.isInteger(video.playerSize[0]) && Number.isInteger(video.playerSize[1])) {
+          adUnit.sizes = video.playerSize;
+        } else {
+          utils.logError('Detected incorrect configuration of mediaTypes.video.playerSize.  Please specify only one set of dimensions in a format like: [640, 480]. Removing invalid mediaTypes.video.playerSize property from request.');
+          delete adUnit.mediaTypes.video.playerSize;
+        }
+      }
+    }
+
+    if (mediaTypes && mediaTypes.native) {
+      const native = mediaTypes.native;
+      if (native.image && native.image.sizes && !Array.isArray(native.image.sizes)) {
+        utils.logError('Please use an array of sizes for native.image.sizes field.  Removing invalid mediaTypes.native.image.sizes property from request.');
+        delete adUnit.mediaTypes.native.image.sizes;
+      }
+      if (native.image && native.image.aspect_ratios && !Array.isArray(native.image.aspect_ratios)) {
+        utils.logError('Please use an array of sizes for native.image.aspect_ratios field.  Removing invalid mediaTypes.native.image.aspect_ratios property from request.');
+        delete adUnit.mediaTypes.native.image.aspect_ratios;
+      }
+      if (native.icon && native.icon.sizes && !Array.isArray(native.icon.sizes)) {
+        utils.logError('Please use an array of sizes for native.icon.sizes field.  Removing invalid mediaTypes.native.icon.sizes property from request.');
+        delete adUnit.mediaTypes.native.icon.sizes;
+      }
+    }
+  });
+  return adUnits;
+}
+
 exports.callBids = (adUnits, bidRequests, addBidResponse, doneCb) => {
   if (!bidRequests.length) {
     utils.logWarn('callBids executed with no bidRequests.  Were they filtered by labels or sizing?');
diff --git a/src/native.js b/src/native.js
index bfe4b64405d..6c8ac266471 100644
--- a/src/native.js
+++ b/src/native.js
@@ -85,6 +85,18 @@ export function nativeBidIsValid(bid, bidRequests) {
     return false;
   }
 
+  if (deepAccess(bid, 'native.image')) {
+    if (!deepAccess(bid, 'native.image.height') || !deepAccess(bid, 'native.image.width')) {
+      return false;
+    }
+  }
+
+  if (deepAccess(bid, 'native.icon')) {
+    if (!deepAccess(bid, 'native.icon.height') || !deepAccess(bid, 'native.icon.width')) {
+      return false;
+    }
+  }
+
   const requestedAssets = bidRequest.nativeParams;
   if (!requestedAssets) {
     return true;
diff --git a/test/spec/native_spec.js b/test/spec/native_spec.js
index 977575a4d19..fa57ceed5f5 100644
--- a/test/spec/native_spec.js
+++ b/test/spec/native_spec.js
@@ -1,5 +1,5 @@
 import { expect } from 'chai';
-import { fireNativeTrackers, getNativeTargeting } from 'src/native';
+import { fireNativeTrackers, getNativeTargeting, nativeBidIsValid } from 'src/native';
 const utils = require('src/utils');
 
 const bid = {
@@ -44,3 +44,113 @@ describe('native.js', () => {
     sinon.assert.calledWith(triggerPixelStub, bid.native.clickTrackers[0]);
   });
 });
+
+describe('validate native', () => {
+  let bidReq = [{
+    bids: [{
+      bidderCode: 'test_bidder',
+      bidId: 'test_bid_id',
+      mediaTypes: {
+        native: {
+          title: {
+            required: true,
+          },
+          body: {
+            required: true,
+          },
+          image: {
+            required: true,
+            sizes: [150, 50],
+            aspect_ratios: [150, 50]
+          },
+          icon: {
+            required: true,
+            sizes: [50, 50]
+          },
+        }
+      }
+    }]
+  }];
+
+  let validBid = {
+    adId: 'test_bid_id',
+    adUnitCode: '123/prebid_native_adunit',
+    bidder: 'test_bidder',
+    native: {
+      body: 'This is a Prebid Native Creative. There are many like it, but this one is mine.',
+      clickTrackers: ['http://my.click.tracker/url'],
+      icon: {
+        url: 'http://my.image.file/ad_image.jpg',
+        height: 75,
+        width: 75
+      },
+      image: {
+        url: 'http://my.icon.file/ad_icon.jpg',
+        height: 2250,
+        width: 3000
+      },
+      clickUrl: 'http://prebid.org/dev-docs/show-native-ads.html',
+      impressionTrackers: ['http://my.imp.tracker/url'],
+      title: 'This is an example Prebid Native creative'
+    }
+  };
+
+  let noIconDimBid = {
+    adId: 'test_bid_id',
+    adUnitCode: '123/prebid_native_adunit',
+    bidder: 'test_bidder',
+    native: {
+      body: 'This is a Prebid Native Creative. There are many like it, but this one is mine.',
+      clickTrackers: ['http://my.click.tracker/url'],
+      icon: {
+        url: 'http://my.image.file/ad_image.jpg',
+        height: 0,
+        width: 0
+      },
+      image: {
+        url: 'http://my.icon.file/ad_icon.jpg',
+        height: 2250,
+        width: 3000
+      },
+      clickUrl: 'http://prebid.org/dev-docs/show-native-ads.html',
+      impressionTrackers: ['http://my.imp.tracker/url'],
+      title: 'This is an example Prebid Native creative'
+    }
+  };
+
+  let noImgDimBid = {
+    adId: 'test_bid_id',
+    adUnitCode: '123/prebid_native_adunit',
+    bidder: 'test_bidder',
+    native: {
+      body: 'This is a Prebid Native Creative. There are many like it, but this one is mine.',
+      clickTrackers: ['http://my.click.tracker/url'],
+      icon: {
+        url: 'http://my.image.file/ad_image.jpg',
+        height: 75,
+        width: 75
+      },
+      image: {
+        url: 'http://my.icon.file/ad_icon.jpg',
+        height: 0,
+        width: 0
+      },
+      clickUrl: 'http://prebid.org/dev-docs/show-native-ads.html',
+      impressionTrackers: ['http://my.imp.tracker/url'],
+      title: 'This is an example Prebid Native creative'
+    }
+  };
+
+  beforeEach(() => {});
+
+  afterEach(() => {});
+
+  it('should reject bid if no image sizes are defined', () => {
+    let result = nativeBidIsValid(validBid, bidReq);
+    expect(result).to.be.true;
+    result = nativeBidIsValid(noIconDimBid, bidReq);
+    expect(result).to.be.false;
+    result = nativeBidIsValid(noImgDimBid, bidReq);
+    expect(result).to.be.false;
+  });
+});
diff --git a/test/spec/unit/core/adapterManager_spec.js b/test/spec/unit/core/adapterManager_spec.js
index 95a249263b5..d349dc2a6da 100644
--- a/test/spec/unit/core/adapterManager_spec.js
+++ b/test/spec/unit/core/adapterManager_spec.js
@@ -1,5 +1,6 @@
 import { expect } from 'chai';
 import AdapterManager from 'src/adaptermanager';
+import { checkBidRequestSizes } from 'src/adaptermanager';
 import { getAdUnits } from 'test/fixtures/fixtures';
 import CONSTANTS from 'src/constants.json';
 import * as utils from 'src/utils';
@@ -816,4 +817,191 @@ describe('adapterManager tests', () => {
       })
     });
   });
+
+  describe('isValidBidRequest', () => {
+    describe('positive tests for validating bid request', () => {
+      beforeEach(() => {});
+
+      afterEach(() => {});
+      it('should main adUnit structure and adUnits.sizes is replaced', () => {
+        let fullAdUnit = [{
+          sizes: [[300, 250], [300, 600]],
+          mediaTypes: {
+            banner: {
+              sizes: [[300, 250]]
+            },
+            video: {
+              playerSize: [640, 480]
+            },
+            native: {
+              image: {
+                sizes: [150, 150],
+                aspect_ratios: [140, 140]
+              },
+              icon: {
+                sizes: [75, 75]
+              }
+            }
+          }
+        }];
+        let result = checkBidRequestSizes(fullAdUnit);
+        expect(result[0].sizes).to.deep.equal([640, 480]);
+        expect(result[0].mediaTypes.video.playerSize).to.deep.equal([640, 480]);
+        expect(result[0].mediaTypes.native.image.sizes).to.deep.equal([150, 150]);
+        expect(result[0].mediaTypes.native.icon.sizes).to.deep.equal([75, 75]);
+        expect(result[0].mediaTypes.native.image.aspect_ratios).to.deep.equal([140, 140]);
+
+        let noOptnlFieldAdUnit = [{
+          sizes: [[300, 250], [300, 600]],
+          mediaTypes: {
+            banner: {
+              sizes: [[300, 250]]
+            },
+            video: {
+              context: 'outstream'
+            },
+            native: {
+              image: {
+                required: true
+              },
+              icon: {
+                required: true
+              }
+            }
+          }
+        }];
+        result = checkBidRequestSizes(noOptnlFieldAdUnit);
+        expect(result[0].sizes).to.deep.equal([[300, 250]]);
+        expect(result[0].mediaTypes.video).to.exist;
+
+        let mixedAdUnit = [{
+          sizes: [[300, 250], [300, 600]],
+          mediaTypes: {
+            video: {
+              context: 'outstream',
+              playerSize: [400, 350]
+            },
+            native: {
+              image: {
+                aspect_ratios: [200, 150],
+                required: true
+              }
+            }
+          }
+        }];
+        result = checkBidRequestSizes(mixedAdUnit);
+        expect(result[0].sizes).to.deep.equal([400, 350]);
+        expect(result[0].mediaTypes.video).to.exist;
+      });
+    });
+
+    describe('negative tests for validating bid requests', () => {
+      beforeEach(() => {
+        sinon.stub(utils, 'logError');
+      });
+
+      afterEach(() => {
+        utils.logError.restore();
+      });
+
+      it('should throw error message and delete an object/property', () => {
+        let badBanner = [{
+          sizes: [[300, 250], [300, 600]],
+          mediaTypes: {
+            banner: {
+              name: 'test'
+            }
+          }
+        }];
+        let result = checkBidRequestSizes(badBanner);
+        expect(result[0].sizes).to.deep.equal([[300, 250], [300, 600]]);
+        expect(result[0].mediaTypes.banner).to.be.undefined;
+        sinon.assert.called(utils.logError);
+
+        let badVideo1 = [{
+          sizes: [[600, 600]],
+          mediaTypes: {
+            video: {
+              playerSize: '600x400'
+            }
+          }
+        }];
+        result = checkBidRequestSizes(badVideo1);
+        expect(result[0].sizes).to.deep.equal([[600, 600]]);
+        expect(result[0].mediaTypes.video.playerSize).to.be.undefined;
+        expect(result[0].mediaTypes.video).to.exist;
+        sinon.assert.called(utils.logError);
+
+        let badVideo2 = [{
+          sizes: [[600, 600]],
+          mediaTypes: {
+            video: {
+              playerSize: ['300', '200']
+            }
+          }
+        }];
+        result = checkBidRequestSizes(badVideo2);
+        expect(result[0].sizes).to.deep.equal([[600, 600]]);
+        expect(result[0].mediaTypes.video.playerSize).to.be.undefined;
+        expect(result[0].mediaTypes.video).to.exist;
+        sinon.assert.called(utils.logError);
+
+        let badVideo3 = [{
+          sizes: [[600, 600]],
+          mediaTypes: {
+            video: {
+              playerSize: [[640, 480]]
+            }
+          }
+        }];
+        result = checkBidRequestSizes(badVideo3);
+        expect(result[0].sizes).to.deep.equal([[600, 600]]);
+        expect(result[0].mediaTypes.video.playerSize).to.be.undefined;
+        expect(result[0].mediaTypes.video).to.exist;
+        sinon.assert.called(utils.logError);
+
+        let badNativeImgSize = [{
+          mediaTypes: {
+            native: {
+              image: {
+                sizes: '300x250'
+              }
+            }
+          }
+        }];
+        result = checkBidRequestSizes(badNativeImgSize);
+        expect(result[0].mediaTypes.native.image.sizes).to.be.undefined;
+        expect(result[0].mediaTypes.native.image).to.exist;
+        sinon.assert.called(utils.logError);
+
+        let badNativeImgAspRat = [{
+          mediaTypes: {
+            native: {
+              image: {
+                aspect_ratios: '300x250'
+              }
+            }
+          }
+        }];
+        result = checkBidRequestSizes(badNativeImgAspRat);
+        expect(result[0].mediaTypes.native.image.aspect_ratios).to.be.undefined;
+        expect(result[0].mediaTypes.native.image).to.exist;
+        sinon.assert.called(utils.logError);
+
+        let badNativeIcon = [{
+          mediaTypes: {
+            native: {
+              icon: {
+                sizes: '300x250'
+              }
+            }
+          }
+        }];
+        result = checkBidRequestSizes(badNativeIcon);
+        expect(result[0].mediaTypes.native.icon.sizes).to.be.undefined;
+        expect(result[0].mediaTypes.native.icon).to.exist;
+        sinon.assert.called(utils.logError);
+      });
+    });
+  });
 });