PURPOSE: We wanted to report the usefulness of both hip AP views, which are some of the various radiographs that are used as a primary diagnostic method for identifying the pistol grip deformity of the femur. MATERIALS AND METHODS: There were 27 cases in patients who were from 20 to 50 years old and who had undergone arthroscopic treatment for femoroacetabular impingement (5 cases of both femoroacetabular impingement) from March 2004 to March 2006, Their preoperative radiographs (both hip APs, the frog leg lateral, the groin lateral and the false profile) were investigated; the most narrow point of the femoral neck, the diameter of the femoral head, the length of the femoral head at the midpoint of these two lines (which is assumed to be the anterosuperior prominence of the femoral neck) were measured on both hip AP views. 15 persons of the same age and who didn't have hip joint pain were chosen as the control group (30 cases) and the same measures was performed and then retrospectively compared with the FAI group. RESULTS: In the FAI group, the femoral head diameter was 53.45 mm, the minimal femoral neck length was 37.58 mm and the femoral head length at the midpoint was 41.52 mm. In the control group, the femoral head diameter was 53.38 mm, the minimal femoral neck length was 35.43 mm and the femoral head length at the midpoint was 39.03 mm. The ratio of the femoral head diameter to the minimal femoral neck length was 0.67 in the FAI group and it was 0.65 in the control group; this was similar in both groups. Yet the ratio of the femoral head diameter to the femoral head length at the midpoint was 0.84 in the FAI group and this was 0.75 in the control group (p=0.01). CONCLUSION: We tried to define the actual value that allows physicians to estimate the pistol grip deformity on both hip AP view of the patients who have hip joint pain, and the ratio of the femoral head diameter to the minimal femoral neck length can be a useful primary indicator for diagnosing femoroactabular impingement when this is over 0.8.