diff --git a/monai/transforms/spatial/array.py b/monai/transforms/spatial/array.py
index 75a25459e8..f0cf047aa6 100644
--- a/monai/transforms/spatial/array.py
+++ b/monai/transforms/spatial/array.py
@@ -285,11 +285,16 @@ def __call__(
 class Flip(Transform):
     """
     Reverses the order of elements along the given spatial axis. Preserves shape.
-    Uses ``np.flip`` in practice. See numpy.flip for additional details.
-    https://docs.scipy.org/doc/numpy/reference/generated/numpy.flip.html
+    Uses ``np.flip`` in practice. See numpy.flip for additional details:
+    https://docs.scipy.org/doc/numpy/reference/generated/numpy.flip.html.
 
     Args:
         spatial_axis: spatial axes along which to flip over. Default is None.
+            The default `axis=None` will flip over all of the axes of the input array.
+            If axis is negative it counts from the last to the first axis.
+            If axis is a tuple of ints, flipping is performed on all of the axes
+            specified in the tuple.
+
     """
 
     def __init__(self, spatial_axis: Optional[Union[Sequence[int], int]]) -> None:
@@ -567,6 +572,9 @@ def __call__(
 class Rotate90(Transform):
     """
     Rotate an array by 90 degrees in the plane specified by `axes`.
+    See np.rot90 for additional details:
+    https://numpy.org/doc/stable/reference/generated/numpy.rot90.html.
+
     """
 
     def __init__(self, k: int = 1, spatial_axes: Tuple[int, int] = (0, 1)) -> None:
@@ -575,6 +583,7 @@ def __init__(self, k: int = 1, spatial_axes: Tuple[int, int] = (0, 1)) -> None:
             k: number of times to rotate by 90 degrees.
             spatial_axes: 2 int numbers, defines the plane to rotate with 2 spatial axes.
                 Default: (0, 1), this is the first two axis in spatial dimensions.
+                If axis is negative it counts from the last to the first axis.
         """
         self.k = k
         spatial_axes_ = ensure_tuple(spatial_axes)
diff --git a/tests/test_rotate90.py b/tests/test_rotate90.py
index a8b4e3f57c..4ab39d5cf6 100644
--- a/tests/test_rotate90.py
+++ b/tests/test_rotate90.py
@@ -37,11 +37,11 @@ def test_k(self):
         self.assertTrue(np.allclose(rotated, expected))
 
     def test_spatial_axes(self):
-        rotate = Rotate90(spatial_axes=(0, 1))
+        rotate = Rotate90(spatial_axes=(0, -1))
         rotated = rotate(self.imt[0])
         expected = []
         for channel in self.imt[0]:
-            expected.append(np.rot90(channel, 1, (0, 1)))
+            expected.append(np.rot90(channel, 1, (0, -1)))
         expected = np.stack(expected)
         self.assertTrue(np.allclose(rotated, expected))