A series of 23 confirmed cases of pyonephrosis initially treated by percutaneous nephrostomy drainage were reviewed. Presentation was extremely variable, ranging from sepsis to asymptomatic bacteriuria. Fever, flank pain and leukocytosis were often absent. Ultrasonography was diagnostic in only 3 of 12 patients. In all, 17 patients had associated nephrolithiasis, and 5 patients ultimately required nephrectomy. Renal urine cultures were positive in 16 of 21 instances, with multiple organisms found in 8 of 21, and added bacteriological data not provided by bladder urine cultures in 11 cases. A pre-existing history of urinary tract infection, hypertension and malignancy was common. Percutaneous drainage was a safe, quick and effective diagnostic and therapeutic method.