This review analyzes several aspects of asymptomatic bacteriuria in patients with diabetes mellitus, including prevalence, bacteriology, coexistent risk factors, localization, natural history, and treatment. The prevalence of asymptomatic bacteriuria is threefold higher among diabetic women than among nondiabetic women. However, rates among diabetic and nondiabetic men are similar. Studies consistently document that the prevalence of asymptomatic bacteriuria is not influenced by the type or duration of diabetes or by the quality of diabetic control. The microorganisms causing asymptomatic bacteriuria in persons with diabetes mellitus are similar to those causing bacteriuria in nondiabetic individuals. More than half of diabetic patients with asymptomatic bacteriuria have upper urinary tract involvement. The long-term consequences of asymptomatic bacteriuria in patients with diabetes mellitus are poorly documented. Clinical trials describing the treatment of asymptomatic bacteriuria in this population suggest that a 2-week course of therapy is equivalent to a 6-week course for the initial eradication of bacteriuria and that, following treatment, reinfection rather than relapse usually occurs. Important questions remaining include whether asymptomatic bacteriuria should be treated in this population and what the optimal antimicrobial regimen is.