Peri-implant diseases are inflammatory lesions which may affect the peri-implant mucosa only (peri-implant mucositis) or also result in loss of supporting bone (peri-implantitis). Peri-implantitis may lead to loss of the implant. Diagnosis of peri-implant disease requires the use of conventional probing to identify the presence of bleeding on probing, and suppuration, both signs of clinical inflammation. Radiographs are required to detect loss of supporting bone. Baseline probing measurements and radiographs should be obtained once the restoration of the implant is completed to allow longitudinal monitoring of peri-implant conditions. Two cross-sectional reports from Sweden indicate that the prevalence of peri-implant disease is high. Smokers and patients who have a history of periodontitis are more at risk for peri-implant disease. The main goal of treatment of peri-implant disease is to control the infection and to prevent disease progression. A number of studies have documented the successful treatment of peri-implant mucositis combining mechanical debridement and chemical plaque control. There is evidence supporting antimicrobial treatment regimens in combination with non-surgical or surgical debridement for peri-implantitis treatment. Long-term data to support these treatment protocols is limited. Whilst it is possible to treat peri-implantitis, prevention is the goal of supportive therapy.