The available evidence suggests that genetic factors have a major role in osteoarthritis. It has been believed for over 50 years that a strong genetic component to certain forms of osteoarthritis is present. This genetic influence has now been estimated to be up to 65% in a recent twin study. The nature of the genetic influence in osteoarthritis is speculative and may involve either a structural defect (that is, collagen), alterations in cartilage or bone metabolism, or alternatively a genetic influence on a known risk factor for osteoarthritis such as obesity. Exciting work has showed that mutations in the collagen type 2 are important in some rare, familial forms of osteoarthritis. Further work is needed on isolating the gene or genes involved in the pathogenesis of this common, disabling condition.