Urinary tract infections (UTI) are among the most common infections afflicting man. Urinary tract infections in young adult women are usually uncomplicated, but are often recurrent and cause considerable morbidity. Urinary tract infections in pregnant women, elderly patients, and catheterized patients warrant special attention because of their association with increased morbidity and possibly with increased mortality. Diagnosis of UTI is usually based on quantitation of uropathogens in voided urine. The traditional criteria for significant bacteriuria, greater than or equal to 10(5) uropathogens per ml of voided urine, is insensitive for detecting acute symptomatic cystitis in men and women and should be replaced with a lower colony count threshold.