A 49-year-old female was followed up at the gynecology clinic after conization for cervical cancer and underwent routine cervical smear, which revealed a cluster of adenocarcinoma cells. Positron emission tomography-computed tomography (PET-CT) showed increased FDG uptake around the proximal urethra. Urethroscopy showed a tumor arising from the urethral diverticulum, and it was revealed to be clear cell adenocarcinoma by cold-cup biopsy. Then, she was referred to our hospital for the treatment of the urethral cancer arising from the urethral diverticulum. MRI showed the urethral diverticulum at circumference of the urethra and a tumor projecting into its lumen. The patient underwent urethrectomy together with resection of the diverticulum tumor and cutaneous vesicostomy. Pathological examination demonstrated pT2, clear cell adenocarcinoma of the urethra. The patient had no local recurrence or metastasis 5 months after the surgery.