The prevalence of perimplant diseases is high and increases visibly. In a recent systematic review of Derks and Tomasi the weighted mean prevalences of periimplant mucositis and peri-implantitis are 43% and 22% respectively. The present state of research does not give us predictable, evidence based treatment strategies for peri-implantitis therefore prevention has to be our goal. We know, that mucositis precedes peri-implantitis and is reversible if treated early. If we want to prevent peri-implantitis we have to look for the etiology and the predisposing factors. Etiological factor of all peri-implant diseases is the biofilm. But local and systemic factors determine development and severity of these diseases. Smoking, diabetes, bad oral hygiene, periodontal disease in the patient’s history, lack of keratinized tissue, implant dependent factors, excess of cementum and prosthetic failures are some of them. So prevention of peri-implantitis starts just before the insertion of the implant, is continued by a proper prosthetic treatment