Aims: All health care systems in the developed world are facing everincreasing health care costs and faced with this prospect, governments and other health care payers seek greater beneþts from existing health resources. An inexpensive alternative without excessive technical demands on physicians or operating room personnel, is two-dimensional (2D) computerassisted preoperative planning. The purpose of the study was to clinically validate the SYMBIOS X-Rays Preoperative Planning software for preoperative planning of cementless total hip replacement. Methods: For each of the thirty patients with osteoarthritis who underwent a total hip arthroplasty using an uncemented anatomic stem, the manual preoperative planning of the surgeon, the 2D computer-assisted one and the result after the real implantation were compared by an independent observer. Comparisons were based on stem and neck sizes as well as stem and rotation center position, using the deþnitive implantation as the reference standard. Results: There were no statistical differences between the results of the manual and 2D computer-assisted preoperative plans in terms of stem size and neck length (< 1 size) as well as for rotation center positioning (< 5mm) when compared to the deþnitive implantation. Conclusion: Two-dimensional computer-assisted preoperative planning seems to provide results as good as those of the manual procedure with the great advantage of allowing the surgeon to simulate various stem designs and to take into account biomechanical criteria.