One hundred twenty-seven episodes of Staphylococcus aureus bacteriuria were reviewed retrospectively in two hospitals to establish the rate of occurrence, clinical importance, and associated predisposing factors. Staphylococcus aureus was an infrequent urinary isolate, and accounted for only about 1% of all positive urine cultures. Although almost all cases in a Veterans Hospital occurred in elderly men, episodes in a community hospital were observed in women and children as well. Patients usually had pyuria (71%) but only 39% had urinary symptoms of fever. Among predisposing factors, serious underlying diseases were uncommon, but urinary tract manipulations or abnormalities were present in nearly two thirds of patients. Fifty-five percent of cases were nosocomial, and 73% of these were associated with urinary catheterization or other invasive urinary tract procedures. Most patients (61%) were not treated for their bacteriuria, and there was a secondary bacteremia rate of 5.5% in the Veterans Hospital. Although infrequently encountered, the presence of S aureus in urine should be treated with at least as much concern as more frequently encountered bacteria.