A case of umbilical endometriosis is presented to highlight the challenges in its diagnosis. The etiology, clinical findings, histologic evaluation, prognosis and treatment options are discussed. While cyclic symptomatology may lend evidence to the diagnosis of umbilical endometriosis, history and clinical findings are often equivocal. Decidualization of umbilical endometriosis can be initially confused with a malignant process on histologic evaluation. The potential for malignant degeneration appears low. Surgical intervention is the treatment of choice.