Coexistence of congenital ureteral diverticulum and hydronephrosis caused by vascular compression is a rare entity. The authors experienced a case of congenital ureteral diverticulum coexistent with hydronephrosis caused by aberrant vascular compression by uterine and umbilical arteries in a 14-year-old girl. The authors could not diagnose accurately this abnormality preoperatively by 3-dimensional computed tomography. After partial ureterectomy, including resection of the saccular lesion and ureteroneocystostomy, the frequency of urinary tract infection decreased.