Of 582 patients who underwent percutaneous nephrolithotomy, 4% had complications. The most common complications were fever (23%) and bleeding necessitating transfusion (12%). Extravasation was seen in 7% of patients and transient ureteral obstruction in 6%. Other complications included pneumothorax or hydrothorax, pneumonia/atelectasis, paralytic ileus, nephrostomy-tube dislodgment or urine drainage from the flank lasting more than 1 week, significant infection, urinoma formation, renal pelvic laceration, ureteral avulsion, ureteropelvic or ureteral stricture, bowel injury, or escape of stone fragments into the retroperitoneum. Seven patients (1%) required immediate surgery: four to repair renal pelvic lacerations, one to repair a ureteral avulsion, and two to control bleeding after nephrostomy-tube removal when embolization failed. Four patients required delayed surgery for ureteral or ureteropelvic junction strictures, which may have been caused by a tissue reaction to the stones rather than by the procedure itself. There were two deaths--one from respiratory failure in a patient with severe interstitial pulmonary fibrosis and chronic renal failure and the other from myocardial infarction in an obese diabetic patient with hypertension.