&NA;Studies of vesicoureteral reflux in a primate model were reviewed. Reflux was found to be uncommon in adults but frequent in infants, suggesting that maturation of the ureterovesical junction occurs. Repeated bladder infections did not prevent this maturation. Infection did not cause reflux unless the junction was only marginally competent. Reflux prolonged urinary tract infection in the infant, but in the adult monkey it did not.