diff --git a/vcr/errors.py b/vcr/errors.py
index bdc9701..f762e8c 100644
--- a/vcr/errors.py
+++ b/vcr/errors.py
@@ -1,5 +1,30 @@
 class CannotOverwriteExistingCassetteException(Exception):
-    pass
+    def __init__(self, *args, **kwargs):
+        message = self._get_message(kwargs["cassette"], kwargs["failed_request"])
+        super(CannotOverwriteExistingCassetteException, self).__init__(message)
+
+    def _get_message(self, cassette, failed_request):
+        """Get the final message related to the exception"""
+        # Get the similar requests in the cassette that
+        # have match the most with the request.
+        best_matches = cassette.find_requests_with_most_matches(failed_request)
+        # Build a comprehensible message to put in the exception.
+        best_matches_msg = ""
+        for best_match in best_matches:
+            request, _, failed_matchers_assertion_msgs = best_match
+            best_matches_msg += "Similar request found : (%r).\n" % request
+            for failed_matcher, assertion_msg in failed_matchers_assertion_msgs:
+                best_matches_msg += "Matcher failed : %s\n" "%s\n" % (
+                    failed_matcher,
+                    assertion_msg,
+                )
+        return (
+            "Can't overwrite existing cassette (%r) in "
+            "your current record mode (%r).\n"
+            "No match for the request (%r) was found.\n"
+            "%s"
+            % (cassette._path, cassette.record_mode, failed_request, best_matches_msg)
+        )
 
 
 class UnhandledHTTPRequestError(KeyError):
diff --git a/vcr/stubs/__init__.py b/vcr/stubs/__init__.py
index c01ba59..05490bb 100644
--- a/vcr/stubs/__init__.py
+++ b/vcr/stubs/__init__.py
@@ -230,11 +230,8 @@ class VCRConnection(object):
                 self._vcr_request
             ):
                 raise CannotOverwriteExistingCassetteException(
-                    "No match for the request (%r) was found. "
-                    "Can't overwrite existing cassette (%r) in "
-                    "your current record mode (%r)."
-                    % (self._vcr_request, self.cassette._path,
-                       self.cassette.record_mode)
+                    cassette=self.cassette,
+                    failed_request=self._vcr_request
                 )
 
             # Otherwise, we should send the request, then get the response
diff --git a/vcr/stubs/tornado_stubs.py b/vcr/stubs/tornado_stubs.py
index b675065..5beea4b 100644
--- a/vcr/stubs/tornado_stubs.py
+++ b/vcr/stubs/tornado_stubs.py
@@ -75,10 +75,8 @@ def vcr_fetch_impl(cassette, real_fetch_impl):
                     request,
                     599,
                     error=CannotOverwriteExistingCassetteException(
-                        "No match for the request (%r) was found. "
-                        "Can't overwrite existing cassette (%r) in "
-                        "your current record mode (%r)."
-                        % (vcr_request, cassette._path, cassette.record_mode)
+                        cassette=cassette,
+                        failed_request=vcr_request
                     ),
                     request_time=self.io_loop.time() - request.start_time,
                 )