Between September 1984 and April 1988, 56 children underwent surgery for an obstructive uropathy discovered on antenatal ultrasound examination. These included 31 cases of stenosis of the pyelo-ureteral junction (PUJ), 9 cases of vesicorenal reflux, 6 mega-ureters (MU), 6 ureteroceles, 3 posterior urethral valves and 1 ectopic ureteral orifice. Major reflux (type III and IV) was included within the obstructive uropathy classification in that it opposes the normal pressure gradient which ensures progression of urine towards the bladder. The nature of the obstruction, morphological study of the kidneys and the renal function itself were very precisely studied and monitored (IVU, ultrasound, isotope tests, DTPA with frusemide and DMSA). In 46 children reconstructive and conservative surgery was possible. Analysis of the various groups of uropathy showed that: 1. Stenosis of the JPU had a very favorable or sometimes spectacular outcome both functionally and morphologically. 2. Cases of reflux showed excellent results, except in the presence of preexisting major renal dysplasia. 3. Mega-ureters had a less good prognosis. Renal growth depended above all on the degree of renal dysplasia which was often associated. 4. This was also true for sever forms of posterior urethral valves. A discussion follows which tries to reply to the following questions: 1. Why does early surgery for stenosis of the JPU give better results? 2. On the other hand, why is the same benefit not obtained in the other obstructive uropathies?