Using criteria adopted by the US Preventive Services Task Force, we evaluated use of the dipstick urinalysis to screen for bacteriuria. When the leukocyte esterase and nitrite dipstick tests are combined, the positive predictive value for detecting bacteriuria exceeded 12% in groups with a 5% or higher prevalence of bacteriuria: women who are pregnant, diabetic, or over 60 years of age and all institutionalized elderly. Conventional antimicrobial regimens for asymptomatic bacteriuria have proved efficacious only for pregnant women. We conclude that pregnant women should be screened for bacteriuria, but with the more sensitive urine culture, because treatment prevents serious fetal and maternal sequelae. Dipstick screening may be justified in women who are over 60 years of age or diabetic. The prevalence of bacteriuria in other groups is too low to justify screening.