Reconstruction of the anterior cruciate ligament is a delicate task for which many different techniques have been proposed. A system consisting of a computer and a three-dimensional optical sensor is proposed to help the surgeon control the placement of a graft. This system can be used to minimize anisometry of the graft and avoid notch impingement. The same system, which had been validated by previous testing on 20 fresh human anatomic specimen knees, was tested on 23 patients who had an anterior cruciate ligament injury. Tunnel placement was performed using the standard technique of Morgan et al and was measured with the computer based system. It was found that all cases had different configurations of tibial and femoral placement. The computer based anisometry measurements ranged from 1.9 mm to 8.8 mm in the anterior part of the graft, and from 1 mm to 13 mm in the centers of the tunnels. Using the computer retrospectively, it was possible to find configurations of the graft in all cases that avoid notch impingement, with anisometry values ranging from 1.3 mm to 3.7 mm. This study shows that a computer based system can be a useful tool for routine anterior cruciate ligament reconstruction and can be useful for research purposes.