diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index fe7ca6fa5c9b1..c9184f148e5a9 100755
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -4882,6 +4882,9 @@ def where(self, cond, other=NA, inplace=False):
         -------
         wh: DataFrame
         """
+        if not hasattr(cond,'shape'):
+            raise ValueError('where requires an ndarray like object for its condition')
+
         if isinstance(cond, np.ndarray):
             if cond.shape != self.shape:
                 raise ValueError('Array onditional must be same shape as self')
@@ -4901,6 +4904,21 @@ def where(self, cond, other=NA, inplace=False):
         rs = np.where(cond, self, other)
         return self._constructor(rs, self.index, self.columns)
         
+    def mask(self, cond):
+        """
+        Returns copy of self whose values are replaced with nan if the
+        inverted condition is True
+
+        Parameters
+        ----------
+        cond: boolean DataFrame or array
+
+        Returns
+        -------
+        wh: DataFrame
+        """
+        return self.where(~cond, NA)
+
 _EMPTY_SERIES = Series([])
 
 
diff --git a/pandas/tests/test_frame.py b/pandas/tests/test_frame.py
index aec7ddffd84e4..dcc7bcb909cd4 100755
--- a/pandas/tests/test_frame.py
+++ b/pandas/tests/test_frame.py
@@ -5220,6 +5220,18 @@ def test_where(self):
         err2 = cond.ix[:2, :].values
         self.assertRaises(ValueError, df.where, err2, other1)
 
+        # invalid conditions
+        self.assertRaises(ValueError, df.mask, True)
+        self.assertRaises(ValueError, df.mask, 0)
+
+    def test_mask(self):
+        df = DataFrame(np.random.randn(5, 3))
+        cond = df > 0
+
+        rs = df.where(cond, np.nan)
+        assert_frame_equal(rs, df.mask(df <= 0))
+        assert_frame_equal(rs, df.mask(~cond))
+
 
     #----------------------------------------------------------------------
     # Transposing