The effect of vesical dysfunction on the survival and function of renal transplants was evaluated by a retrospective study in which 18 children with posterior urethral valves and 18 children with vesicoureteral reflux were randomly matched with 36 children used as controls. There was no statistically significant difference in patient survival among the 3 groups. Five years after transplantation 50 per cent of the grafts in children with posterior urethral valves were functioning, while 73 and 75 per cent, respectively, of the grafts were functioning in children with vesicoureteral reflux and in the control group. Renal function during the 5 years was significantly better in children in the control group and in those with vesicoureteral reflux than in children with posterior urethral valves. We believe that the presence of an abnormal bladder may alter graft survival and adversely affect the function of the transplanted kidney.