Asymptomatic bacteriuria is a condition in which a urine culture has more than 100,000 colonies per ml and in which the patient has no symptoms. There is a startling prevalence of this condition in the elderly population. Uncertainty exists about both the need and the nature of possible therapy for asymptomatic bacteriuria in the elderly. Adequate studies do not define well the associated morbidity or mortality of this condition in the patient without obstruction. When obstruction is present, therapy is necessary until the obstruction is relieved.