A 54-year-old female underwent exploratory laparotomy for evaluation of a large abdominopelvic mass. She was found to have a 29-pound multicystic tumor arising from the right ovary. There were no other gross intraabdominal abnormalities. Histologic examination of the mass revealed a mucinous cystadenocarcinoma of low malignant potential and a mature cystic teratoma. To our knowledge, this is the first case report of an ovarian epithelial adenocarcinoma of low malignant potential associated with a mature cystic teratoma.