Fourteen patients with posterior urethral valves and end-stage renal failure were urodynamically evaluated in order to identify and correct any bladder dysfunction before renal transplant. Of the 14 patients, during filling, six had normal bladder function, two had an over-distended bladder (one with instability), one had instability, four had poor compliance, and one had a very reduced bladder capacity. During the voiding phase, one had a myogenic failure and another had detrusor-sphincteric dyssynergia. Four patients underwent bladder augmentation. Three were managed with anticholinergic therapy and two required clean intermittent catheterization owing to post-voiding residual urine. A renal transplant was performed in all of these patients at a mean age of 8.2 years. We compared outcome in these 14 patients with bladder dysfunction treated before transplantation with outcome in a matched control group of 14 transplant patients. Graft function and survival were similar in both groups. We believe that urodynamic studies must be included in the pretransplant evaluation of patients with posterior urethral valves in order to diagnose any bladder dysfunction and commence appropriate treatment to avoid any negative influence on graft function.