Decreased bone mineral density (BMD) at the hip is an important risk factor for hip fractures, which are a major socioeconomic problem in the elderly. The incidence of congenital hip dysplasia (CHD) is about 7-13% in the Middle European population. We assessed the question of whether a conservatively treated CHD may be a risk factor for low BMD at the hip in adult women. We evaluated prospectively 240 premenopausal women (33 +/- 7 years). Past medical history was recorded including the presence or absence of CHD. Lumbar and femoral BMD using dual-energy X-ray absorptiometry (DXA) and biochemical parameters of bone metabolism were measured. X-rays of the pelvis were performed in CHD patients. Thirty-one (12.9%) of the patients had a history of conservatively treated CHD, four (1.2%) had undergone surgery; all other patients served as control group. Patients and controls were comparable for anthropometric data, lifestyle factors, and hip axis length. BMD in CHD patients was significantly lower at the hip (difference by 1 STD) but comparable at the spine. OC was significantly higher in patients with CHD than in controls. In a logistic regression model, CHD was associated with a 6.3-fold increased risk for low BMD at the hip. We therefore conclude that a history of conservatively treated CHD may be a major risk factor for low BMD at the hip in about 1 out of 10 women. Whether this translates into an increased risk for future hip fractures will have to be assessed in further prospective studies.