Xanthogranulomatous pyelonephritis should be suggested preoperatively in patients with a history of chronic urinary tract infection and certain roentgenographic findings. These include: (1) unilateral renal enlargement, either localized or diffuse; (2) renal and/or ureteral calculi, especially large ureteral calculi; (3) nonfunction or very faint opacification of the collecting system on intravenous pyelography; and (4) angiographic demonstration of an avascular mass or masses with stretched, attenuated intrarenal vessels, benign neovascularity at the margins of the mass(es), irregular nephrogram, and prominent capsular and periureteric vessels.