Mucinous borderline ovarian tumor (MBT) affects a wide age range with a mean age at diagnosis of about 50 years. Presentation includes abdominal mass (usually unilateral), abdominal pain and distention. Most cases are confined to the ovary (Stage I) at the time of diagnosis. Acellular mucin is sometimes found on peritoneal surface, but peritoneal implants are uncommon. The image shows an ovarian MBT. The glandular structures are lined by intestinal-type epithelium with mild to moderate cytologic atypia. The appearance resembles a hyperplastic colonic polyp.