We report a case retroperitoneal mature teratoma showing an abnormally high CA19-9 (carbohydrate antigen 19-9) serum level in a 30-year-old woman. She was hospitalized for an episode of left upper abdominal pain. High CA19-9 tissue level and immunohistochemical findings were found in removed tissue. This case is the third report of a CA19-9-producing teratoma and literature was reviewed and discussed.