Acetabular dysplasia (AD) contributes to the development of osteoarthritis of the hip. A rotational acetabular osteotomy (RAO) is one of the methods of pelvic osteotomy to prevent or treat secondary osteoarthritis of the hip. Although most of the patients that undergo RAO show satisfactory results, some have poor results. This study investigated whether gene polymorphisms of both the vitamin D receptor (VDR) and oestrogen receptor (ER) are involved in both AD and the postoperative results following RAOs. Sixty-four Japanese patients with AD who were treated by an RAO were enrolled in this study (59 women and 5 men, aged 13-59, with an average age of 40.3). Gene polymorphisms of the VDR [ApaI and TaqI restriction fragment length polymorphisms (RFLPs)] and ER (PvuII and XbaI RFLPs) were determined in these patients. The relationship between both the AD and radiographic postoperative changes of the hip joint after an RAO with these gene polymorphisms were examined. The frequencies of ER gene polymorphism coded as pp (RFLP/PvuII) in patients with AD were statistically significantly different (p = .011) from those coded as both PP and Pp. The joint space width narrowed even after RAO in 90% of the patients with the pp gene polymorphism, while it narrowed in only 35% of the patients with either PP or Pp seven years or longer after an RAO. The PvuII polymorphism in the ER gene was associated with the postoperative result of an RAO, while no association was observed between the AD with VDR and ER gene polymorphisms.