diff --git a/litellm/llms/mongodb/common_utils.py b/litellm/llms/mongodb/common_utils.py
index c2d081b8d8d..bf3bf953772 100644
--- a/litellm/llms/mongodb/common_utils.py
+++ b/litellm/llms/mongodb/common_utils.py
@@ -181,6 +181,7 @@ def translate_mongo_error(error: Exception, index_name: str, database: str, coll
     try:
         from pymongo.errors import (
             ConfigurationError,
+            ConnectionFailure,
             ExecutionTimeout,
             InvalidOperation,
             NetworkTimeout,
@@ -202,6 +203,14 @@ def translate_mongo_error(error: Exception, index_name: str, database: str, coll
             f"The MongoDB vector search against '{database}.{collection}' timed out before returning. "
             f"Driver detail: {error}"
         )
+    # ServerSelectionTimeoutError and NetworkTimeout both sit under ConnectionFailure, so this
+    # only sees what those two branches left: a dropped or refused connection
+    if isinstance(error, ConnectionFailure):
+        return config_error(
+            f"The connection to '{database}.{collection}' was refused or dropped. On Atlas this is "
+            "usually a connection string with no username and password, or a TLS failure. Confirm "
+            f"the URI is the one Atlas shows under Connect, Drivers. Driver detail: {error}"
+        )
     if isinstance(error, OperationFailure):
         code: Final = error.code
         detail: Final = str(error).lower()
@@ -247,4 +256,11 @@ def translate_mongo_error(error: Exception, index_name: str, database: str, coll
         )
     if isinstance(error, InvalidOperation):
         return config_error(f"The MongoDB client was already closed or is unusable. Driver detail: {error}")
+    # pymongo's URI parser raises a plain ValueError, not a PyMongoError, for a password holding an
+    # unescaped '/', which would otherwise reach the caller as a 500
+    if isinstance(error, ValueError):
+        return config_error(
+            "mongodb_connection_string could not be parsed. A username or password containing "
+            f"'@', '/', ':' or '%' has to be percent-encoded per RFC 3986. Driver detail: {error}"
+        )
     return error
diff --git a/tests/test_litellm/llms/mongodb/vector_stores/test_mongodb_transformation.py b/tests/test_litellm/llms/mongodb/vector_stores/test_mongodb_transformation.py
index 668fa676692..d60504c31e5 100644
--- a/tests/test_litellm/llms/mongodb/vector_stores/test_mongodb_transformation.py
+++ b/tests/test_litellm/llms/mongodb/vector_stores/test_mongodb_transformation.py
@@ -759,6 +759,42 @@ class TestErrorTranslation:
 
         assert "rejected the credentials" in str(translated)
 
+    def test_a_dropped_connection_is_a_400_not_an_unhandled_driver_error(self):
+        """AutoReconnect sits under ConnectionFailure alongside the two timeout classes, and Atlas
+        answers a URI with no credentials by closing the connection rather than failing auth. Left
+        untranslated it is not a litellm exception type, so it reaches the caller as a 500."""
+        from pymongo.errors import AutoReconnect
+
+        translated = self._translate(AutoReconnect("connection closed"))
+
+        assert isinstance(translated, BadRequestError)
+        assert "refused or dropped" in str(translated)
+        assert "no username and password" in str(translated)
+
+    def test_server_selection_timeout_still_wins_over_the_connection_branch(self):
+        from pymongo.errors import ServerSelectionTimeoutError
+
+        translated = self._translate(ServerSelectionTimeoutError("no servers"))
+
+        assert isinstance(translated, Timeout)
+        assert "refused or dropped" not in str(translated)
+
+    def test_network_timeout_still_wins_over_the_connection_branch(self):
+        from pymongo.errors import NetworkTimeout
+
+        translated = self._translate(NetworkTimeout("socket timed out"))
+
+        assert isinstance(translated, Timeout)
+        assert "refused or dropped" not in str(translated)
+
+    def test_an_unescaped_password_character_is_a_400_not_a_500(self):
+        """pymongo's URI parser raises a plain ValueError, not a PyMongoError, when a password
+        holds an unescaped '/'. That is a routine mistake and it must not be a 500."""
+        translated = self._translate(ValueError("Port contains non-digit characters"))
+
+        assert isinstance(translated, BadRequestError)
+        assert "percent-encoded" in str(translated)
+
     def test_unauthorized_points_at_the_database_user_permissions(self):
         from pymongo.errors import OperationFailure