Purpose: Implant therapy is highly predictable and successful. However, certain risk factors can predispose individuals to lower rates of success. The purpose of this systematic review was to evaluate the available literature to assess whether smoking, diabetes, and periodontitis have an adverse affect on the outcomes of implants placed in patients with these conditions. Materials and Methods: The dental literature was searched using the MEDLINE, Cochrane Collaboration, and EMBASE databases. Using specific inclusion and exclusion criteria, 2 reviewers evaluated titles, abstracts, and full articles to identify articles relevant to this review. All searches were conducted for articles published through May 2005. Data from included articles for each of the risk factor groups, smoking, diabetes, and periodontitis, were abstracted and analyzed. Results: A detailed search of the literature and evaluation of relevant articles identified 35 articles for inclusion in this systematic review. Nineteen articles were identified for smoking, 4 articles were identified for diabetes, and 13 articles were identified for periodontitis. One article met the criteria for both smoking and periodontitis. Implant survival and success rates were reported for smokers versus nonsmokers; diabetic patients versus nondiabetic patients; and patients with a history of treated periodontitis versus patients with no history of periodontitis. The findings revealed statistically significant differences in survival and success rates for smokers (better for nonsmokers), with greater differences observed when the data were analyzed according to bone quality (less for loose trabecular bone). No difference in implant survival rate was found between patients with and without diabetes. Likewise, no difference in implant survival rates was found between patients with a history of treated periodontitis compared to patients with no history of periodontitis. Conclusions: The results of this systematic review of the literature demonstrated that smoking has an adverse affect on implant survival and success. The effect of smoking on implant survival appeared to be more pronounced in areas of loose trabecular bone. Type 2 diabetes may have an adverse effect on implant survival rates, but the limited number of studies included in this review do not permit a definitive conclusion. A history of treated periodontitis does not appear to adversely affect implant survival rates but it may have a negative influence on implant success rates, particularly over longer periods. Keywords: dental implants, dental implant survival, diabetes, periodontitis, smoking, tobacco