Background We used a stereologic method based on 3D CT scanning to estimate the projected load-bearing surface in the hip joint.Patients and methods 6 normal hip joints and 6 dysplastic hips were examined. The latter were CT-scanned before and after periacetabular osteotomy.Results We found that the average area of the projected load-bearing surface of the femoral head preoperatively was 7.4 (6.5–8.4) cm²and postoperatively 11 (9.8–14) cm², which was similar to the load-bearing surface in the normal control group. We performed double measurements and the coefficient of error of the mean was estimated at 1.6%. Due to overprojection, an overestimation of about 3.8% on the projected loadbearing surface occurred. Consequently, the stereologic method proved to be precise and unbiased.Interpretation Our findings indicate that this method is of value for monitoring the load-bearing area in the hip joint of patients undergoing periacetabular osteotomy.