The relationship between pelvic tilt and acetabular femoral head covering was determined in 38 patients with decreased lumbar lordosis. Posterior pelvic tilt and acetabular femoral head covering were measured on radiographs taken in both supine and standing positions. Previously reported normal values obtained from 96 patients were used as controls. Posterior pelvic tilt increased (P<.01) in patients with decreased lumbar lordosis and anterior acetabular femoral head covering decreased (P<.0001) compared with the controls. These differences were more remarkable in the standing position than in the supine position. Patients with decreased lumbar lordosis have decreased femoral head covering, especially in the standing position.