We report two cases of clear cell adenocarcinoma arising in the urethral diverticulum. Case 1 occurred in a 79-year-old woman presenting with complaints of frequent micturition. Magnetic resonance imaging (MRI) revealed a localized urethral diverticular tumor. Transurethral resection of the tumor was performed, and the final histopathological diagnosis was clear cell adenocarcinoma. Anterior pelvic exenteration was performed. She had no recurrence 15 months after surgery. Case 2 occurred in a 79-year-old woman presenting with urinary incontinence. As in Case 1, MRI and histopathological findings of transurethral resection of the tumor revealed clear cell adenocarcinoma in the urethral diverticulum. Anterior pelvic exenteration and ileal conduit formation were performed. She had no recurrence 16 months after surgery. Clear cell adenocarcinoma in the urethral diverticulum is very rare. We review 17 cases of clear cell adenocarcinoma arising in the urethral diverticulum in Japan.