A ureteral diverticulum which appears as an outpunch from the ureter wall is a rare clinical finding with unclear etiology. We report on a 29- year-old woman whose first presentation was a recurrent urinary tract infection. A left pelvic cyst was disclosed by abdominal ultrasonography and computed tomography scanning. A diverticulum of the left distal ureter was the final diagnosis following a series studies. Surgical intervention revealed that the left ureter was draining into the diverticulum but that there was no communication between the diverticulum and the urinary bladder. Because of the presence of a muscular layer, the pathologist confirmed it to be a true diverticulum. To the best of our knowledge, no such case of a ureteral diverticulum in adults has been reported.