diff --git a/stackprinter/__init__.py b/stackprinter/__init__.py
index 94ae70c..15022a4 100644
--- a/stackprinter/__init__.py
+++ b/stackprinter/__init__.py
@@ -151,7 +151,7 @@ def format(thing=None, **kwargs):
         return fmt.format_stack_from_frame(thing, **kwargs)
     elif isinstance(thing, Thread):
         return format_thread(thing, **kwargs)
-    elif isinstance(thing, Exception):
+    elif isinstance(thing, BaseException):
         exc_info = (thing.__class__, thing, thing.__traceback__)
         return format(exc_info, **kwargs)
     elif _is_exc_info(thing):
diff --git a/tests/test_exception_instances.py b/tests/test_exception_instances.py
new file mode 100644
index 0000000..bb5910f
--- /dev/null
+++ b/tests/test_exception_instances.py
@@ -0,0 +1,47 @@
+from io import StringIO
+
+import pytest
+
+import stackprinter
+
+
+def _raise_exception(exc):
+    raise exc
+
+
+@pytest.mark.parametrize('exception_type', [
+    BaseException, KeyboardInterrupt, SystemExit, GeneratorExit,
+    Exception, ValueError,
+])
+@pytest.mark.parametrize('with_traceback', [False, True])
+@pytest.mark.parametrize('options', [
+    {}, {'style': 'darkbg', 'suppressed_exceptions': []},
+])
+def test_exception_instance_matches_exc_info(exception_type, with_traceback,
+                                             options):
+    exc = exception_type('message')
+    if with_traceback:
+        try:
+            _raise_exception(exc)
+        except BaseException:
+            pass
+
+    exc_info = (type(exc), exc, exc.__traceback__)
+    expected = stackprinter.format(exc_info, show_vals=None, **options)
+    assert exception_type.__name__ in expected
+    assert 'message' in expected
+    if with_traceback:
+        assert '_raise_exception' in expected
+
+    assert stackprinter.format(exc, show_vals=None, **options) == expected
+    output = StringIO()
+    stackprinter.show(exc, file=output, show_vals=None, **options)
+    assert output.getvalue() == expected + '\n'
+
+
+@pytest.mark.parametrize('thing', [
+    42, 'message', object(), [], BaseException, KeyboardInterrupt, ValueError,
+])
+def test_format_rejects_non_exception_instances(thing):
+    with pytest.raises(ValueError, match='Expected an exception instance'):
+        stackprinter.format(thing)