A case of renal pseudoaneurysm which occurred as a complication of percutaneous nephrolithotomy (PNL) for right renal staghorn calculi is presented. A 59-year-old man, who previously had left nephrectomy due to renal staghorn calculi and right pyelolithotomy due to renal calculi, was admitted to our hospital for treatment of recurrent right renal staghorn calculi on March 29, 1990. Laboratory data on admission revealed no significant abnormality except for a mild elevation on blood glucose (116 mg/dl). Pseudomonas aeruginosa (10(6) CFU/ml) was cultured from urine. Preoperative plain abdominal film showed right partial staghorn calculi extending to the lower calyx and pelvis. Three sessions of PNL were performed. Two nephrostomy tubes were placed in the upper and middle calyces at the first session. Although all calculi were removed completely, massive renal bleeding with bladder tamponade occurred several times postoperatively and blood transfusion was necessary. Renal angiography was performed, and it was demonstrated renal pseudoaneurysm at the upper nephrostomy tract. At the same time the pseudoaneurysm was treated by superselective embolization with an absorbable gelatin sponge. We reviewed the related literature on complications of PNL. Etiology and treatment of a renal vascular injury associated with PNL are also discussed.