We report a case of ectopic ureterocele in a male adult found during examination of a traumatic injury. A 26-year-old man sustained a blow to his left back during a football game and was admitted to the hospital with a complaint of abdominal pain. The computed tomographic scan showed a huge cystic mass in the retroperitoneum. A cystoscope revealed a large bulge from the left ureteral orifice to the bladder neck and another ureteral orifice distal to the bulge. Retrograde pyelography revealed an ectopic ureterocele showing a complete duplication, a lateral deviation of the left ureter and a bladder deviation to the right. An ectopic ureteral orifice was opening in the posterior urethra. An ureteral catheter inserted into this orifice revealed a dilated left ureter from the upper half of the kidney. Because the function of left upper of kidney was maintained, a transurethral incision was performed. Vesicoureteral reflux remained, but the postoperative course was uneventful. We discuss 11 cases of ectopic ureterocele in male adults including this case.