Osteoarthritis (OA) is the most common type of arthritis and is frequently associated with significant disability. Its public health impact is increasing due to the aging of the population and the obesity epidemic. The Johnston County Osteoarthritis Project is an ongoing, population-based prospective cohort begun in 1990 to fill knowledge gaps about prevalence, incidence, and progression of OA, and its risk factors, in African American and Caucasian men and women in North Carolina. Critically important phenotypic differences were observed in patterns of multi-joint OA burden, with African Americans much less likely than Caucasians to have hand OA and much more likely to have multiple large joint involvement. Racial differences also exist in systemic bone and joint tissue biomarkers. Novel potentially modifiable risk factors identified in this cohort include selenium and blood lead levels. Selected key findings of this ongoing study will be discussed.