This article examines current radiologic imaging and interventional techniques used in the diagnosis and initial treatment of pyonephrosis. Included is a review of all pyonephrotic series published in the English literature since 1970. Although the authors found that two thirds of pyonephrotic kidneys are still removed at surgery, there is an increasing emphasis on preservation of renal function. Percutaneous nephrostomy provides an excellent tool for drainage of pus and determination of residual renal function prior to definitive surgery.