To compare endourologic and open surgical management of a failed pyeloplasty in children.A total of 478 pts underwent pyeloplasty between January 1997 and December 2005. Of these, 30 (6.3%) had a secondary UPJO which was managed by retrograde endopyelotomy (RE) in 18 and re-do pyeloplasty (RP) in 12. Age, stent placement/type at initial pyeloplasty, symptoms at presentation for secondary UPJO, hospital stay, complications and success rate (SR) were compared between the 2 groups. Success was defined as radiographic relief of obstruction, as determined by ultrasound or diuretic renography at the latest follow-up (F/U). An indwelling ureteral stent was placed in all pts and removed 8-12 weeks postoperatively.Mean F/U after primary surgery was 15.8 (3-60) months for RE and 47 (3-108) for RP. Mean age at RE was 7.4 (2-14) yrs and at RP 7.3 (1-17). Mean F/U after RE was 47 (15-132) months and after RP 33.1 (12-78). RP was performed through a flank approach (10 dismembered/2 ureterocalycostomy). RE technique consisted of laser, laser+balloon dilatation and cautery wire balloon (CWB) in 6, 4 and 8 pts respectively. RP was successful in all cases and RE failed in 55.6% (4- stricture >1cm / 4- <3 yrs of age). CWB endopyelotomy failed in 7 of 8 pts (p=0.05). After failed RE (n=10), 3 pts underwent RP (SR=100%), 2 antegrade endopyelotomy (SR=50%) and 5 repeated RE (SR=40%). All these children remain free of obstruction.VariablesRE n=18 (%)RP n=12 (%)pAge < 3 yrs4 (22.2)4 (33.3)NSInternal/ext stent3 (16.6)3 (25)No stent5 (27.7)2 (16.6)Double J10 (55.5)7 (58.3)Pyelonephritis4 (22.2)3 (25)Obstruction18 (100)12 (100)Abdominal pain9 (50)5 (41.6)Admission (days)1.32.9NSComplications01 leakageSuccess rate8 (44.4)12 (100)0.005Single RE had a significantly lower success rate than RP after a failed pyeloplasty in children. We speculate that CWB RE, long strictures and age less than 3 yrs are bad prognostic factors for success in treatment of a secondary UPJO.