We compared the results of the first 56 consecutive percutaneous corrections of ureteropelvic junction obstruction (endopyelotomy) at our institution with the most recent 32 consecutive cases of open pyeloplasty. The percutaneous procedure required less time (average 89.4 minutes versus 106.4 minutes for an open operation) and entailed less postoperative pain (60 per cent of the patients required an average of 4.7 unit doses of narcotics, whereas 88 per cent of the pyeloplasty patients required an average of 10.3 unit doses). The average hospital stay was less after endopyelotomy (average 6.2 versus 10.0 days) and return to normal activity occurred more quickly (average 19.8 versus 41.5 days). Endopyelotomy was successful in 87.5 per cent of the patients, with all failures being apparent within 6 weeks and they were easily correctable by traditional methods. Reported success rates of pyeloplasty ranged from 95 to 98 per cent.