Two adjacent genes on the 12q chromosome, the alpha 1 chain of Type II collagen, and the vitamin D receptor, have been considered potentially related to the pathophysiology of osteoarthritis. Two restriction fragment length polymorphisms were detected in 50 healthy donors and in 143 patients having a total hip replacement for idiopathic osteoarthritis or osteoarthritis secondary to developmental hip dysplasia. The polymorphic sites of Type II collagen and vitamin D receptor were amplified by polymerase chain reaction, and the products were digested with PvuII and BsmI restriction enzymes, respectively. The results showed that medical history and clinical characteristics, including gender, familial history of osteoarthritis, other hip prosthesis, and how early in life implantation was done did not seem to be connected to a particular genotype. Significant results were found by assessing the two groups of diseases that led to hip arthroplasty, suggesting a possible link between some haplotypes and the risk of severe osteoarthritis in patients with hip dysplasia. These results indicate that genetic markers could contribute to the understanding of the natural history of this disease.