Perinephric abscess is a rare condition; it may be acute, but can take a chronic and atypical course as a result of incomplete treatment with antibiotics. In this case the diagnosis is often delayed. The most common cause is primary renal disease, with perforating ureteric stones, abscess-forming pyelonephritis, renal carbuncle and pyonephrosis as the most important factors. Diagnosis depends on a varying combination of clinical signs, any of which is not necessarily present and which is not pathognomic, but nevertheless, in their totality, are fairly typical. Characteristic are pain on percussion and pressure, resistance in the renal angle and fever. Laboratory investigations do not contribute to the diagnosis. These only show findings typical of any infection, and frequently a marked anaemia. An infected urine may be suggestive. The traditional clinical and radiological methods may well indicate a space-occupying lesion, but its further elucidation depends on angiography. Renal and perinephric abscesses must be distinguished from other space-occupying renal lesions. Abscesses can usually be distinguished from cysts because they are generally less clearly demarkated and often show a hypervascular margin with a "blush". A further differential diagnosis of perinephic abscess is a peri-renal haematoma. Radiologically, an haematoma also produces a perirenal mass with displacement and compression of the kidney. As with perinephric abscesses, the angiogram shows dilatation and displacement of the capsular arteries. Differences in the neovascularity, as well as in the clinical symptoms, permit differentiation between abscesses and hypovascular carcinomas in most cases, or at least suggest the probable diagnosis.