Our current knowledge of the long-term outcome of uncomplicated urinary tract infections in women is based on several things: a reevaluation of the criteria for defining pyelonephritis at autopsy, careful description of the causes of renal disease among patients entering dialysis and transplant programs, long-term observation of patients, and epidemiologic studies attempting to determine the association of bacteriuria with mortality. The weight of the evidence favors the conclusion that, although urinary tract infections can severely impair renal function, this is rare in the absence of a major predisposing factor such as obstruction, calculus, reflux, abnormalities of the voiding mechanism, or diabetes. The predisposing lesions, however, may go undetected until heralded by episodes of acute pyelonephritis or by renal failure. Unfortunately, urinary tract infections are so common that it is difficult to distinguish the population at greatest risk. The possible role of renal damage produced by autoimmune mechanisms following infection needs continued study.