It is possible to transform an external diversion (transcolic cutaneous ureterostomy) into an internal one (uretero-sigmoido-sigmoidostomy) in cases of bladder exstrophy which have not been reconstructed. This must not be done at too early an age (not before 7) and only under certain conditions : good renal function, normal upper urinary tract, no sigmoido-ureteral reflux good anal sphincter. Such an operation radically changes the life of the exstrophic who was previously handicapped by a collecting apparatus. One must assure a careful long term follow-up. The major details of technique and the results of 20 cases are described.