We have evaluated the incidence, prevalence, predisposing factors and evolution of urinary tract infection (UTI) developing late after transplantation in 63 patients whose graft had lasted at least 3 months and whose follow-up averaged 7 years. Beyond 3 months after transplantation incidence of UTI decreases progressively, from 25 to 0%, 50% of the patients remaining free of infection throughout the period of observation. Neither the original kidney disease except perhaps diabetic nephropathy nor the presence of vesicoureteral reflux were predisposing factors. Incidence and prevalence in females were twice that in male. Late UTI did not affect graft or patient survival, or graft function at 5 years. Most UTI were asymptomatic and had a benign course. However, in 3 patients septicemia or graft dysfunction ensued demonstrating the need for continuous monitoring of urine cultures.