A 54-year-old female was referred to us for a nodule under her umbilical region. The nodule had enlarged slowly and reached a size of 20 mm in diameter over the last 2 years. She had no symptoms and there was no oozing of blood or pain during menstruation. The nodule was removed under lumbar anesthesia. Histological examination of the resected nodule revealed an island of glandular tissue in the deep dermis, which was composed of a single layer of columnar cells, and was diagnosed as umbilical endometriosis. There was no associated lesion in the intrauterine or pelvic space. There has not been any evidence of recurrence five months postoperatively. On finding an umbilical mass in women, this rare disease must be considered.