Purpose: Altering the vertical dimension of occlusion (VDO) by increasing the interarch distance is common in oral rehabilitation, but little is known about the ability of implant patients, who lack sensory perception in implanted regions, to adapt to such changes. This study sought to evaluate the outcome of increasing VDO in patients restored with implant-supported fixed restorations opposed by restored natural teeth or implant-supported restorations. Materials and Methods: VDO was increased by 3 to 5 mm to address the individual prosthetic needs of 30 patients. Group A (control) consisted of 10 patients with fixed restorations on natural dentition that opposed the natural dentition in a new VDO relationship. Two test groups consisted of 10 patients each, with fixed implant-supported restorations opposing either the restored natural dentition (group B) or fixed implant-supported restorations (group C). After an average follow-up of 66 months, marginal bone changes were calculated using standardized periapical radiographs, and mechanical prosthetic maintenance data were collected from patient files. The results were analyzed using Kruskal-Wallis one-way analysis of variance to identify significant differences between the groups. Results: All patients successfully adapted to the new VDO. Two patients in group B and four in group C reported tooth clenching or grinding, which abated after 2 to 3 months (P < .05). More bone loss and tooth failures were observed in group A, and more mechanical complications, such as porcelain fractures, were observed in group C (P < .05). Conclusion: Within the limitations of this study, alteration of VDO was an acceptable procedure in patients with implant-supported fixed restorations, but precautions should be taken to prevent mechanical problems. Int J Oral Maxillofac Implants 2009;24:497–501