Accurate United States data on the prevalence of low-back pain (LBP) and its related medical care would assist health care planners, policy makers, and investigators. Data from the second National Health and Nutrition Examination Survey (NHANES II) were analyzed to provide such information. The cumulative lifetime prevalence of LBP lasting at least 2 weeks was 13.8%. In univariate analyses, important variations in prevalence were found by age, race, region, and educational status. Most persons with LBP sought care from general practitioners, with orthopaedists and chiropractors being the next most common sources of care. Sources of care, and in some cases therapy, varied among demographic subgroups. These data demonstrate substantial nonbiologic influences on the prevalence and treatment of LBP, and suggest an agenda for health services researchers.