The authors reviewed 20 cases of xanthogranulomatous pyelonephritis. An accurate preoperative diagnosis of this disease is difficult because of its clinical and radiologic similarities to various other renal lesions. A resistant urinary tract infection in a patient with a nonfunctioning kidney and a perinephric abscess should lead to the condition being suspected. Although xanthogranulomatous pyelonephritis is mainly a histologic diagnosis, computerized tomography opens new perspectives in the preoperative determination. This could allow less radical surgery in selected cases.