Group B Streptococcus (GBS) is a well-known cause of infection in the perinatal and puerperal periods, but its role as a urinary tract pathogen of adults in nonobstetric situations has not yet been defined. We carried out a prospective 19-month study of all nonpregnant adult patients with significant GBS bacteriuria. This microorganism accounted for 2% of positive urine cultures. Our series included 60 patients, 85% of whom were women and 95% of whom had at least one underlying condition. Urinary tract abnormalities (60%) and chronic renal failure (27%) were among the most frequent underlying problems. The infection was community acquired in 65% of cases. Clinical manifestations were related equally to the upper and the lower urinary tract (37% and 38% of cases, respectively). The clinical outcome was poor in 18% of episodes despite treatment. All isolates were sensitive to all antibiotics tested except gentamicin. We conclude that GBS is a significant urinary pathogen in nonpregnant adults and that its presence signals a need for screening for urinary tract abnormalities.