diff --git a/monai/transforms/utility/dictionary.py b/monai/transforms/utility/dictionary.py
index e7cf63e210..63ed6ec305 100644
--- a/monai/transforms/utility/dictionary.py
+++ b/monai/transforms/utility/dictionary.py
@@ -675,8 +675,6 @@ def __init__(self, keys: KeysCollection, name: str, dim: int = 0, allow_missing_
 
         """
         super().__init__(keys, allow_missing_keys)
-        if len(self.keys) < 2:
-            raise ValueError("Concatenation requires at least 2 keys.")
         self.name = name
         self.dim = dim
 
diff --git a/tests/test_concat_itemsd.py b/tests/test_concat_itemsd.py
index 520833fc88..9c51e1efea 100644
--- a/tests/test_concat_itemsd.py
+++ b/tests/test_concat_itemsd.py
@@ -38,6 +38,20 @@ def test_numpy_values(self):
         np.testing.assert_allclose(result["img1"], np.array([[0, 1], [1, 2]]))
         np.testing.assert_allclose(result["cat_img"], np.array([[1, 2], [2, 3], [1, 2], [2, 3]]))
 
+    def test_single_numpy(self):
+        input_data = {"img": np.array([[0, 1], [1, 2]])}
+        result = ConcatItemsd(keys="img", name="cat_img")(input_data)
+        result["cat_img"] += 1
+        np.testing.assert_allclose(result["img"], np.array([[0, 1], [1, 2]]))
+        np.testing.assert_allclose(result["cat_img"], np.array([[1, 2], [2, 3]]))
+
+    def test_single_tensor(self):
+        input_data = {"img": torch.tensor([[0, 1], [1, 2]])}
+        result = ConcatItemsd(keys="img", name="cat_img")(input_data)
+        result["cat_img"] += 1
+        torch.testing.assert_allclose(result["img"], torch.tensor([[0, 1], [1, 2]]))
+        torch.testing.assert_allclose(result["cat_img"], torch.tensor([[1, 2], [2, 3]]))
+
 
 if __name__ == "__main__":
     unittest.main()