Ureteropelvic junction obstruction in children: evolution of diagnosis and treatment. 180 hydronephrosis due to ureteropelvic junction obstruction in 162 patients have been referred to our hospital. The patients were all infants and children with an age ranging between 1 day to 15 years. Out of 9 abstinences (grade I or 11) and 7 nephrectomies for destroyed kidneys (3 of them after temporary nephrostomy), we performed 164 ureteropelvic junction resections and anastomosis, 51 of them with associated pyeloplasty. The use of a stenting catheter passing through the anastomosis and coming out as a nephrostomy in 81 cases gave us 5 mechanical complications while the complete absence of drainage gave only 3 fistulaes. 2 of these fistulaes had a spontaneous rapid healing after endoscopic ureteral catheterism. Out of 160 follow-up cases, we reoperated 6 failures with success: 5 ureteropelvic reanastomoses and one ureterocalycostomy. This study shows us that the early treatment due to antenatal ultrasound diagnosis improves the prognosis. Renal scanning with furosemide test permits to specify the surgical indication in limited cases and the presence of a residual obstruction in case of persistance of renal pelvis dilatation in the postoperative period. The posterior approach and the absence of internal drainage simplify the treatment, improve the patient comfort and limit the hospitalisation period to 5 days.