Objective To investigate the imaging diagnosis of acetabular dysplastic coxarthrosis. Method The imaging of the acetabular dysplasia was analyzed in 51 patients (87 hips). All but four patients were women. The age ranged from 22 to 78 years, and the mean age was 42.6 years. Pelvis radiographs were studied in all cases, and CT scan was performed in 18 cases and MRI in 10 cases. Results The fundamental signs on the plain film included shallow acetabulum, increased obliquity and insufficient coverage of the femoral head by the acetabulum. The CE angles were determined in all the cases, ranging from -10? to 30?, mean 12.9?. The charp angles ranged from 35? to 67?, mean 45.3?. The secondary osteoarthritis were revealed in 75 hips (84.2%). 54 hips (62.1%) had cyst like lesions in weight bear area of the acetabulum or femoral head. 19 hips had subluxation of femoral head. CT and MRI displayed small cystlike lesions and forward shift of the femoral head, which could not be shown on plain film, respectivly in 13 and 10 hips. Conclusion The cyst like lesion of subarticular region is a common sign in acetabular dysplastic coxarthrosis. CT or MRI can show the early osteolytic lesion and forward subluxations.