Osteoarthritis (OA) is now recognized as a major public health problem. The risk of OA depends upon factors that increase generalized susceptibility to the disorder, as well as biomechanical factors that modify risk at specific joint sites. Occupational physical activity is one of the important influences in this latter category. Epidemiological evidence has begun to mount that occupational physical activity is a determinant of the risk of knee and hip OA. Occupations that involve regular knee bending and heavy lifting confer a greater likelihood of developing knee OA, while there appears to be a particular propensity for hip OA among farmers. Further research into these relationships will have two important consequences: (1) The issue whether industrial recompense is justified for workers in these industries who develop OA will be clarified. (2) A clearer understanding of the pathophysiology of these relationships will lead to more effective preventive strategies.