Purpose: Endopyelotomy has been proposed as a technique to treat ureteropelvic junction obstruction after failed open pyeloplasty. However, to our knowledge no long-term results of this treatment have been reported. We report the long-term followup of a cohort of patients in whom pyeloplasty failed and who subsequently were treated with endopyelotomy. Materials and Methods: From January 1985 to February 1996, 72 patients in whom open surgical pyeloplasty failed were treated with percutaneous endopyelotomy. Mean patient age was 35 years (range 5 to 82). The interval between pyeloplasty and subsequent failure ranged from 2 months to 30 years (mean 57 months). The major presenting symptoms were pain in 82% of cases, fever and urinary tract infections in 37.5%, stone formation in 25% and gross hematuria in 21%. Results: Antegrade endopyelotomy using a hooked knife was performed in all patients with no unusual difficulty and minimal complications. A total of 63 patients (87.5%) had long lasting clinical and radiographic treatment success after a mean followup of 88.5 months. Of the 9 endopyelotomy failures (12.5%) 7 (77.8%) were detected immediately after stent removal at 6 weeks, 1 (11.1%) at 6 months and 1 (11.1%) at 10 months postoperatively (mean failure inter-val 3.3 months). The failures were corrected with repeat endopyelotomy in 1 patient, pyeloplasty in 3, ileal interposition in 1 and nephrectomy in 4. Conclusions: Endopyelotomy is the treatment of choice for recurrent ureteropelvic junction obstruction after failed pyeloplasty, with a high and sustained long-term success rate and no reported new failures after 1-year followup. Furthermore, endopyelotomy is technically easier with less morbidity than repeat open pyeloplasty.