Until the last decade, coagulase-negative staphylococci occurring in urine specimens were usually regarded as a contaminant. In the early 1970s, i.e., more than ten years after the original demonstration of Staphylococcus saprophyticus in urine specimens, this species became recognized as a frequent cause of urinary tract infections (UTI). In young women, S. saprophyticus is, after Escherichia coli, the second-most-frequent causative agent of acute UTI. Patients with UTI caused by S. saprophyticus usually present with symptomatic cystitis. Signs and symptoms of renal involvement are also often registered. The urine sediment of a patient with UTI caused by S. saprophyticus has a characteristic appearance microscopically. Chemical screening methods for bacteriuria do not always succeed in diagnosing UTI caused by S. saprophyticus. Even when such an infection occurs above the neck of the bladder, low numbers of colony-forming units (less than 10(5) cfu/ml) of S. saprophyticus are comparatively often found in the bladder and voided urine. S. saprophyticus is usually susceptible to antibiotics commonly prescribed for patients with UTI, with the exception of nalidixic acid. The bacterium has a capacity for selective adherence to human urothelium. It causes direct hemagglutination. The adhesin for S. saprophyticus is a lactosamine structure. This staphylococcal species produces an extracellular enzyme complex that can inhibit growth of both gram-positive and gram-negative bacteria.