PURPOSE: We investigated the reference line closer to the true femoral anteversion on only the cutting surface of the proximal femoral neck during the femoral stem insertion in cementless total hip arthroplasty. MATERIALS AND METHODS: A postoperative CT of both hips was taken to observe the positioning of the stem and its correlation with the true anteversion of the contralateral side of 33 consecutive patients after unilateral primary cementless total hip arthroplasty with avascular necrosis of the femoral head. We defined several parameters and measured the true anteversion on the contralateral side and the stem anteversion on the lesion side. RESULTS: The average of the midcortical angle was 13.9 degrees +/-6.8 degrees on the lesion side and 0.1 degrees +/-1.3 degrees less than the true anteversion on the contralateral side. CONCLUSION: The study has shown that anteversion using a midline between the anterior cortical line and the posterior cortical line is compatible with the true femoral anteversion.