This study was designed to determine whether Staphylococcus saprophyticus was an important cause of urinary tract infection (UTI), as has been reported by European, but not by American, investigators, S. saprophyticus was the second most common cause of UTI in young (mean age, 20 years), sexually active female outpatients without known preexisting kidney disease or preceding manipulation of the urinary tract. Most cases presented as acute cystitis, but frank pyelonephritis and UTI in pregnant females were observed. The organism was rarely found as a contaminant in urine cultures. When present in the mucocutaneous flora of the anal-urogenital area, the organism was significantly associated with UTI by the same organism. These results show that S. saprophyticus should be accepted as an important urinary tract pathogen of young female patients in the United States. A simple adequate laboratory identification may be based on resistance to novobiocin (disk diffusion test), absence of hemolysis and coagulase, and intense pigment production (65% of strains yellow, 35% white).