The past several years have brought marked changes in our understanding of the consequences of urinary tract infections (UTIs). Studies of infants with intrauterine dilatation of the urinary tract show that many children previously thought to have incurred kidney damage after an infection actually have congenital renal damage. The importance of vesicoureteric reflux (VUR) in the pathogenesis of acute pyelonephritis has been downgraded with the recognition of the frequency with which kidney infection occurs in the absence of VUR. Some infants with intrauterine VUR and no history of UTI have impaired kidney function or hypertension secondary to renal hypoplasia or dysplasia.