Low-back pain is one of the most prevalent and costly problems facing the U.S. health-care system. Although it is the second most frequent primary complaint reported by patients seeking medical care, there is a dearth of research and a lack of consensus on how to treat low-back pain. Consequently, patients receive a multitude of treatments, many of which may be ineffective and/or inefficient. The purpose of this study is to assess the effectiveness and cost effectiveness of 4 popular management strategies used in the treatment of low-back pain. The study has 6 specific aims: 1) determine which management strategy, chiropractic care or medical care, is more effective in terms of pain reduction, functional status improvement, and patient satisfaction for musculoskeletal low-back pain in a multi-specialty group practice; 2) assess the effectiveness of physical therapy among low-back- pain patients receiving chiropractic or medical care; 3) determine which strategy is the most cost-effective for treating low-back pain; 4) assess the relationship between patient satisfaction with care and other outcome measures, i.c., pain and functional status improvement; S) estimate the effects of occupational factors on low-back-pain outcomes; and 6) estimate the effects of self care on low-back-pain outcomes. The study will be conducted in a 100,000-member multi-specialty group practice over a 5-year period. About 250 ambulatory patients will be randomized to each of 4 treatment groups in a balanced factorial design: chiropractic care with and without physical therapy, and medical care with and without physical therapy. Subjects will be followed for 18 months after the start of treatment with outcome assessments at 2 and 6 wks, and 6, 12, and 18 mos. Sources of data include a physical examination and personal interview at baseline, follow-up questionnaires, exit telephone interviews and provider assessments, medical charts, and computer records. Baseline exams and interviews will obtain a broad array of information on sociodemographic, clinical, psychosocial, and occupational factors. Follow-up questionnaires mailed to participants will address general health status, functional status, low-back-pain severity, recurrence and duration, self care for low-back pain, days of restricted activity and disability. Medical charts and records will be used to obtain data on health-care use and the costs of services for the 18-month follow-up period. Cost-effectiveness analyses will be conducted in two ways: from the perspective of the institution (based on costs of services), and from the perspective of the payer (based on charges). Major strengths of this study are: randomization of eligible patients from a single group practice into 4 treatment groups; inclusion of patients with a broad array of low-back-pain etiologies; comprehensive collection of data on many (nonrandomized) factors that might affect low-back pain; and use of several outcome measures. The results of this project will help elucidate the roles of medical doctors, chiropractors, and physical therapists in the treatment of low-back pain, and they will have important implications to national health-care policy.