The incidence and severity of urinary tract infection episodes were evaluated in two groups of renal transplantation patients. Group 1 consisted of 11 patients transplanted following successful surgical correction of a noninfected vesicoureteral reflux in native kidneys, and group 2 of 28 patients transplanted with a noninfected vesicoureteral reflux. An increased incidence of acute urinary tract infection episodes was noted in group 2 as compared to group 1 (42.8 vs. 18%), with a mean of 2.6 +/- 1.4 episodes per patient in group 2 and 0.5 +/- 0.32 in group 1. Asymptomatic bacteriuria was not statistically different in the two groups (36.4 vs. 25%). In group 2, the incidence of urinary tract infection episodes increased in patients presenting high-grade (3 and 4) reflux in native kidneys. Despite the relatively low number of patients involved, our observations indicate that high-grade vesicoureteral reflux in native kidneys must be operated before transplantation, even when there is no history of urinary tract infections and urine cultures are sterile.