Successful improvement in health in our increasingly aged population will depend in substantial part on reduction of age specific disability levels. In turn, the epidemiologic model suggests that this requires identification of risk factors, development of intervention models, and testing of these models. We attempted to identify risk factors for physical disability among 4,428 50-77-year-olds using baseline data collected in the first National Health and Nutrition Examination Survey (NHANES I) (1971-1975) linked to disability data collected 10 years later in the NHANES I Epidemiologic Followup Study. Results of forward stepwise linear regression analysis showed that the major characteristics contributing to greater disability (explaining at least 1% of the variability in scores) were older age at baseline, less nonrecreational activity, arthritis history, less education, female sex, and greater body mass index at age 40. Other factors associated with greater disability included a history of asthma, cardiovascular disease, abnormal urine test, less recreational activity, higher sedimentation rate, rheumatic fever history, lower caloric intake, positive musculoskeletal findings, histories of polio and allergies, lower family income, elevated blood pressure, lower serum albumin, history of tuberculosis, glucose in the urine, and histories of hip or spine fracture, chronic pulmonary disease, and kidney disease.