Osteoarthritis (OA) is the most common non-inflammatory joint disease. The hip and knee, the main weight-bearing joints, are most commonly affected. Previous trauma to the joints is strongly associated with OA. Participation in various sports activities, including fitness room activities, intensive running and cycling, is on the rise. These activities offer potential health benefits and have been advocated for the primary and secondary prevention of many diseases, including diabetes and coronary artery disease. However, it has been hypothesized that physical activity might increase cartilage degeneration and thus accelerate knee OA. In this article we review the literature with the purpose of evaluating the purported association between sports activity and knee OA. Previous research did not show a significant association between intense physical activity and knee OA in the general population. A strong association was found in cases of former joint injury and in acquired and congenital joint defects. Moderate physical activity is recommended for people already suffering from OA with the goal of increasing muscle-strength, reducing pain and preserving the range of movement in the affected joints. People who wish to participate in sports activities should be evaluated by their family physician. This evaluation should include assessment of risk factors for knee OA, particularly in patients with previous joint injury.