diff --git a/modules/id5IdSystem.js b/modules/id5IdSystem.js
index c585f2fdae0..42f0044edc3 100644
--- a/modules/id5IdSystem.js
+++ b/modules/id5IdSystem.js
@@ -10,6 +10,7 @@ import {
   deepSetValue,
   isEmpty,
   isEmptyStr,
+  isPlainObject,
   logError,
   logInfo,
   logWarn,
@@ -21,8 +22,8 @@ import {getRefererInfo} from '../src/refererDetection.js';
 import {getStorageManager} from '../src/storageManager.js';
 import {uspDataHandler, gppDataHandler} from '../src/adapterManager.js';
 import {MODULE_TYPE_UID} from '../src/activities/modules.js';
-import { GreedyPromise } from '../src/utils/promise.js';
-import { loadExternalScript } from '../src/adloader.js';
+import {GreedyPromise} from '../src/utils/promise.js';
+import {loadExternalScript} from '../src/adloader.js';
 
 /**
  * @typedef {import('../modules/userId/index.js').Submodule} Submodule
@@ -39,6 +40,7 @@ export const ID5_PRIVACY_STORAGE_NAME = `${ID5_STORAGE_NAME}_privacy`;
 const LOCAL_STORAGE = 'html5';
 const LOG_PREFIX = 'User ID - ID5 submodule: ';
 const ID5_API_CONFIG_URL = 'https://id5-sync.com/api/config/prebid';
+const ID5_DOMAIN = 'id5-sync.com';
 
 // order the legacy cookie names in reverse priority order so the last
 // cookie in the array is the most preferred to use
@@ -146,9 +148,17 @@ export const id5IdSubmodule = {
       id5id: {
         uid: universalUid,
         ext: ext
-      }
+      },
     };
 
+    if (isPlainObject(ext.euid)) {
+      responseObj.euid = {
+        uid: ext.euid.uids[0].id,
+        source: ext.euid.source,
+        ext: {provider: ID5_DOMAIN}
+      }
+    }
+
     const abTestingResult = deepAccess(value, 'ab_testing.result');
     switch (abTestingResult) {
       case 'control':
@@ -232,7 +242,7 @@ export const id5IdSubmodule = {
       getValue: function(data) {
         return data.uid
       },
-      source: 'id5-sync.com',
+      source: ID5_DOMAIN,
       atype: 1,
       getUidExt: function(data) {
         if (data.ext) {
@@ -240,6 +250,20 @@ export const id5IdSubmodule = {
         }
       }
     },
+    'euid': {
+      getValue: function (data) {
+        return data.uid;
+      },
+      getSource: function (data) {
+        return data.source;
+      },
+      atype: 3,
+      getUidExt: function (data) {
+        if (data.ext) {
+          return data.ext;
+        }
+      }
+    }
   },
 };
 
diff --git a/test/spec/modules/id5IdSystem_spec.js b/test/spec/modules/id5IdSystem_spec.js
index ecce98d0b8d..af468f2fe4d 100644
--- a/test/spec/modules/id5IdSystem_spec.js
+++ b/test/spec/modules/id5IdSystem_spec.js
@@ -1,5 +1,11 @@
 import * as id5System from '../../../modules/id5IdSystem.js';
-import {coreStorage, getConsentHash, init, requestBidsHook, setSubmoduleRegistry} from '../../../modules/userId/index.js';
+import {
+  coreStorage,
+  getConsentHash,
+  init,
+  requestBidsHook,
+  setSubmoduleRegistry
+} from '../../../modules/userId/index.js';
 import {config} from '../../../src/config.js';
 import * as events from '../../../src/events.js';
 import CONSTANTS from '../../../src/constants.json';
@@ -10,7 +16,7 @@ import {hook} from '../../../src/hook.js';
 import {mockGdprConsent} from '../../helpers/consentData.js';
 import {server} from '../../mocks/xhr.js';
 import {expect} from 'chai';
-import { GreedyPromise } from '../../../src/utils/promise.js';
+import {GreedyPromise} from '../../../src/utils/promise.js';
 
 const IdFetchFlow = id5System.IdFetchFlow;
 
@@ -37,6 +43,22 @@ describe('ID5 ID System', function () {
       'linkType': ID5_STORED_LINK_TYPE
     }
   };
+  const EUID_STORED_ID = 'EUID_1';
+  const EUID_SOURCE = 'uidapi.com';
+  const ID5_STORED_OBJ_WITH_EUID = {
+    'universal_uid': ID5_STORED_ID,
+    'signature': ID5_STORED_SIGNATURE,
+    'ext': {
+      'linkType': ID5_STORED_LINK_TYPE,
+      'euid': {
+        'source': EUID_SOURCE,
+        'uids': [{
+          'id': EUID_STORED_ID,
+          'aType': 3
+        }]
+      }
+    }
+  };
   const ID5_RESPONSE_ID = 'newid5id';
   const ID5_RESPONSE_SIGNATURE = 'abcdef';
   const ID5_RESPONSE_LINK_TYPE = 2;
@@ -886,6 +908,35 @@ describe('ID5 ID System', function () {
       }, {adUnits});
     });
 
+    it('should add stored EUID from cache to bids', function (done) {
+      id5System.storeInLocalStorage(id5System.ID5_STORAGE_NAME, JSON.stringify(ID5_STORED_OBJ_WITH_EUID), 1);
+
+      init(config);
+      setSubmoduleRegistry([id5System.id5IdSubmodule]);
+      config.setConfig(getFetchLocalStorageConfig());
+
+      requestBidsHook(function () {
+        adUnits.forEach(unit => {
+          unit.bids.forEach(bid => {
+            expect(bid).to.have.deep.nested.property(`userId.euid`);
+            expect(bid.userId.euid.uid).is.equal(EUID_STORED_ID);
+            expect(bid.userIdAsEids[0].uids[0].id).is.equal(ID5_STORED_ID);
+            expect(bid.userIdAsEids[1]).is.deep.equal({
+              source: EUID_SOURCE,
+              uids: [{
+                id: EUID_STORED_ID,
+                atype: 3,
+                ext: {
+                  provider: ID5_SOURCE
+                }
+              }]
+            })
+          });
+        });
+        done();
+      }, {adUnits});
+    });
+
     it('should add config value ID to bids', function (done) {
       init(config);
       setSubmoduleRegistry([id5System.id5IdSubmodule]);
@@ -984,6 +1035,13 @@ describe('ID5 ID System', function () {
     it('should return undefined if passed a string', function () {
       expect(id5System.id5IdSubmodule.decode('somestring', getId5FetchConfig())).is.eq(undefined);
     });
+    it('should decode euid from a stored object with EUID', function () {
+      expect(id5System.id5IdSubmodule.decode(ID5_STORED_OBJ_WITH_EUID, getId5FetchConfig()).euid).is.deep.equal({
+        'source': EUID_SOURCE,
+        'uid': EUID_STORED_ID,
+        'ext': {'provider': ID5_SOURCE}
+      });
+    });
   });
 
   describe('A/B Testing', function () {