Summary: A navigation system should improve the quality of a total knee prosthesis implantation in comparison to that obtained with the classic, surgeon-controlled operative technique. The authors implanted 100 total knee prostheses with an infrared navigation system (Orthopilot, Aesculap, Tuttlingen, Germany). The quality of implantation was studied on postoperative long leg coronal and lateral x-rays, and compared with a control group of 100 matched-paired patients operated on with a total knee prostheses implanted using a classic, surgeon-controlled technique. An optimal mechanical femorotibial angle (177-183°) was obtained in 93 cases in the study group and 75 cases in the control group (P <0.05). Similar differences were seen for the coronal and sagittal orientations of both tibial and femoral components. Globally, 67 cases in the study group and 31 cases in the control group were implanted in an optimal manner for all studied criteria (P <0.001). The used navigation system allows significant improvement in the quality of implantation of a total knee prosthesis in comparison to that obtained with classic, surgeon-controlled instrumentation, and long-term outcome might consequently be improved.