Background: Total Hip Arthtroplasty (THA) is a common orthopedic operation and preoperative planning has been reported to be an integral part of THA. The present study was carried out over the patients referring to Akhtar hospital between 1997 and 1999 to determine the efficacy of preoperative planning. Materials and methods: Those undergone unilateral THA, either cemented or noncemented, have entered this descriptive study. Patients' radiographs have preoperatively planned using Muller SLS-88 System and desired indices were compared with postoperative radiographs. Paired Hest was used for statistical analysis. Results: The study population included 21 males and 30 females with mean age of 58.4±12 years. Indices of "inclination" and "anteversion" were not compared, since standard values have been considered. Indices of X and Z that represent T and R lines have shown significant difference, however, the index of Y, representing the distance from the center of rotation to the prominent point of lesser trochanter, showed no significant difference. Thus, the resection lines of femoral neck were balanced according to the surgeon's experience, and finally the position of femoral component was not significantly changed. Conclusion: Preoperative planning is of significant value for the successful performance of THA. A clinical trial is highly recommended.