A unique necropsy specimen of a cecoureterocele, together with the bladder and urethra in a female newborn, was studied to determine the structure of the ureterocele and the accompanying vesicourethral sphincter. The ureterocele within the bladder base and the entire urethra were examined macroscopically and microscopically in serial sections. The ureterocele and its cecal extension were amuscular. The bladder neck, and the involuntary and voluntary sphincters were attenuated or devoid of muscle in the quadrant beneath the ureterocele and its cecal extension. These findings were correlated with the clinical features of 2 living patients with comparable ureteroceles who had urinary incontinence following surgical excision of the ureteroceles.