Purpose: The aim of this study was to identify risk factors for the development of clinical signs of periimplant mucositis and for the presence of periodontal pathogens and to determine a possible correlation between these clinical signs and the presence of periodontal pathogens. Materials and Methods: In 100 patients, a modified Plaque Index (PI), a modified Sulcular Bleeding Index (BOP), and pocket probing depth (PPD) were recorded. Patients with one implant site that scored positive for PI, BOP, and PPD >= 5 mm were considered to have peri-implant mucositis. A sample taken at the implant with the deepest pocket was analyzed for periodontal pathogens. Implant surface roughness, smoking, augmentation at the implant site, type of dentition, and radiation therapy were recorded as possible cofactors in the disease process. Results: Thirty-one patients showed clinical signs of peri-implant mucositis and, in 25 implant sites, periodontal pathogens were found. Smoking showed a statistically significant correlation with clinical signs of peri-implant mucositis (univariate analysis). For periodontal pathogens at the implant site, the type of dentition was statistically significant. In the multivariate analysis of the clinical signs of peri-implant mucositis, smoking and radiation therapy were significant explanatory variables. Seventy-two percent of the patients showed agreement for finding either clinical signs of peri-implant mucositis and periodontal pathogens or for no clinical signs and no pathogens. The sensitivity for diagnosis of peri-implant mucositis was 45%, and the specificity was 84%. Conclusions: Smoking was the most important risk factor in the formation of peri-implant mucositis. Radiation therapy was an explanatory variable for the occurrence of inflammation. Implant surface roughness, augmentation at the implant site, and type of dentition had little influence on clinical signs of peri-implant mucositis. The type of dentition influences the periodontal microbiota at the implant site. Keywords: dental implants, peri-implant mucositis, periodontal pathogens, risk factors