Osteoarthritis (OA) is a heterogeneous disease resulting from multiple pathogenic mechanisms. Several forms of OA are inherited in an autosomal Mendelian pattern. Recent studies have identified a variety of mutations in the type II collagen gene, which encodes the main collagenous component of articular cartilage in some forms of familial OA and other heritable diseases of cartilage, including Stickler syndrome and the chondrodysplasias. Mutations in the type X collagen gene, which encodes a major collagen of growth plate cartilage, have been identified in the Schmid type of osteochondrodysplasias. Identification of additional mutations in cartilage collagen genes in familial OA will broaden our understanding of the pathogenesis of the disease, and may permit the preventive treatment of individuals at risk.