The anatomy of the periodontal tissues of a tooth differs from that of a dental implant. The largest differences are in the lack of a periodontal membrane between the bone and a dental implant and its lack of an organized connective tissue attachment at the collar. These anatomical differences may influence the inflammatory response of each to bacterial plaque. Similarity has been demonstrated between the bacterial plaque on implants and teeth, but the significance of the difference between plaques at healthy and diseased sites on implants has not been determined. The consequence of periodontitis is loss of fibrous tissue attachment to the tooth and loss of supporting bone. A similar loss of supporting bone adjacent to dental implants has also been observed. Regenerative surgical techniques have been developed to reform the fibrous tissue attachment to the tooth and replace the lost supporting bone and these techniques have not been applied to dental implants. Healing and regeneration after periodontitis is now better understood, but regeneration around implants remains controversial. The evidence for the existence of a distinct entity, 'peri-implantitis', and its treatment are discussed.