Symptomatic osteoarthritis(OA) of the knee and hip is common, the leading cause of disability among those 65 years of age and older, and responsible for a large proportion of direct and indirect health costs (1-13). African-Americans may be more likely than Caucasians to develop activity limitation and disability from arthritic (1,4,12,14-19). Previous epidemiologic studies of knee and hip OA, however, have almost exclusively limited to Caucasians. Begun in 1990 in a rural county in North Carolina, the Johnston Country Osteoarthritis Project is a prospective, population- based study of knee, hip, and patellofemoral (PFJ) OA in both African- Americans and Caucasians (20). Extensive baseline clinical, radiographic, functional, and serologic data have been collected on study participants, and significant ethnic differences in radiographic features of OA have been noted (20-24). This proposal aims to re-examine the 3200 study participants, aged 45 years and older an average of 5 years after study entry, to describe ethnic differences in incidence and progression of radiographic knee, hip, and PFJ OA, progression of OA to new joint sites, knee and hip pain, and functional disability. Subgroups at high risk for these outcomes will be identified. The roles of 1) obesity, 2) metabolic and co-morbid cardiovascular factors, and 3) dietary factors, including omega-3 and omega-6 fatty acids and anti-oxidant micronutrients, will be examined longitudinally as potential risk factors for these outcomes in each ethnic group. Dietary data will derive from computer-assisted dietary intake questionnaires and extensive, highly detailed analysis of baseline sera for 14 carotenoids and tocopherols. Stratified analysis and multiple logistic and polytomous logistic regression, with generalized estimating equations when appropriate, will be used to assess ethnic differences in the roles of these factors in the above outcomes. By examining the roles of these factors in multiple aspects of the OA process in both ethnic groups with the same study, efficiency and the amount of information obtained per unit cost can be maximized.