BACKGROUND: Hip osteoarthritis (OA) is a common disabling disease, which has a much higher prevalence in Caucasians than Asians. The reasons for this ethnic difference in prevalence are unknown. Hip OA often is thought to be secondary to morphologic abnormalities. If particular abnormalities predisposing to hip OA occur more frequently in Caucasians, these differences in hip shape could account for prevalence differences. METHODS: A morphometric study was performed using 400 non-osteoarthritic hips of 200 women participants from 2 studies: the Beijing OA study and the SOF study from the U.S. We focused on measures of hip dysplasia and impingement (Lateral Center Edge Angle, Impingement Angle, Acetabular Slope, Femoral Head Neck Ratio and the Cross Over Sign) and compared data from Chinese and Caucasian hips. RESULTS: Compared with their Chinese counterparts, Caucasian women had a lower mean impingement angle (83.6° vs. 87.0° (,) p=.03) and were more likely to have center edge angles suggestive of impingement (for center edge angle >35(o) , 11% of Chinese vs. 23% of Caucasian hips, p = .008). On the other hand, low center edge angles suggesting dysplasia were found more often in Chinese women (for