diff --git a/os_client_config/config.py b/os_client_config/config.py
index aac41a4..87b8d65 100644
--- a/os_client_config/config.py
+++ b/os_client_config/config.py
@@ -263,6 +263,17 @@ class OpenStackConfig(object):
             if not self.default_cloud:
                 self.default_cloud = self.envvar_key
 
+        if not self.default_cloud and self.cloud_config['clouds']:
+            if len(self.cloud_config['clouds'].keys()) == 1:
+                # If there is only one cloud just use it. This matches envvars
+                # behavior and allows for much less typing.
+                # TODO(mordred) allow someone to mark a cloud as "default" in
+                # clouds.yaml.
+                # The next/iter thing is for python3 compat where dict.keys
+                # returns an iterator but in python2 it's a list.
+                self.default_cloud = next(iter(
+                    self.cloud_config['clouds'].keys()))
+
         # Finally, fall through and make a cloud that starts with defaults
         # because we need somewhere to put arguments, and there are neither
         # config files or env vars
diff --git a/os_client_config/tests/test_config.py b/os_client_config/tests/test_config.py
index 09a11d2..4f2bf96 100644
--- a/os_client_config/tests/test_config.py
+++ b/os_client_config/tests/test_config.py
@@ -55,6 +55,25 @@ class TestConfig(base.TestCase):
         self.assertIsInstance(cloud, cloud_config.CloudConfig)
         self.assertEqual(cloud.name, '')
 
+    def test_get_one_cloud_default_cloud_from_file(self):
+        single_conf = base._write_yaml({
+            'clouds': {
+                'single': {
+                    'auth': {
+                        'auth_url': 'http://example.com/v2',
+                        'username': 'testuser',
+                        'password': 'testpass',
+                        'project_name': 'testproject',
+                    },
+                    'region_name': 'test-region',
+                }
+            }
+        })
+        c = config.OpenStackConfig(config_files=[single_conf],
+                                   vendor_files=[self.vendor_yaml])
+        cc = c.get_one_cloud()
+        self.assertEqual(cc.name, 'single')
+
     def test_get_one_cloud_auth_defaults(self):
         c = config.OpenStackConfig(config_files=[self.cloud_yaml])
         cc = c.get_one_cloud(cloud='_test-cloud_', auth={'username': 'user'})
diff --git a/releasenotes/notes/default-cloud-7ee0bcb9e5dd24b9.yaml b/releasenotes/notes/default-cloud-7ee0bcb9e5dd24b9.yaml
new file mode 100644
index 0000000..49aba3c
--- /dev/null
+++ b/releasenotes/notes/default-cloud-7ee0bcb9e5dd24b9.yaml
@@ -0,0 +1,7 @@
+---
+issues:
+  - If there was only one cloud defined in clouds.yaml
+    os-client-config was requiring the cloud parameter
+    be passed. This is inconsistent with how the envvars
+    cloud works which WILL work without setting the cloud
+    parameter if it's the only cloud.