The author recorded the occlusion of 100 patients with fixed implant prostheses on 571 endosseous root form implants when the implants were placed. He made six subsequent occlusal contact comparisons at three-month intervals. Hyperocclusion occurred on implant prostheses in nearly half of the patients during the test period, with the majority of changes occurring in the first three to six months. These changes in the distribution of occlusal contact forces may partially explain the reports of early implant failure by other investigators, and they suggest the need for a more vigorous post-insertion occlusal evaluation.