35 peri-implantitis recently referred for 10 years showed four types of inflammatory lesions, such as mild granulomatous lesion(n=5), severe granulomatous lesion(n=4), severe inflammatory fibrous scar tissue(n=15), severe abscess formation(n=11). However, the inflammatory lesions were usually localized at the peri-implant area accompanying compensatory hyperplasia of fibrous connective tissue. The fibrous scar and the necrotic abscess frequently occurred depend on the severity of inflammatory reaction. Among 30 cases of severe inflammatory lesions, only 2 cases involved condensing osteitis in adjacent alveolar bone. Thus, we suppose that the inflammatory progression of peri-implantitis could be partly inhibited by the hyperplastic fibrous stromal tissue stimulated by implant material. And more, the focal abscess formed around the implant can be easily drainaged through the fibrous tract of implant pathway, resulted in the chronic persistent inflammatory granulomatous lesion, that is contrast to the common socket granuloma after tooth extraction. However, depend on the degree of inflammatory reaction in the peri-implantitis the inflamed fibrous collagenous tissues, unregenerated graft materials, necrotic abscess and sequestra should be removed by surgical intervention and followed by antibiotic therapy, because the peri-implant tissue is as vivid as the normal periodontium for the inflammatory defense system. Therefore, we suggest that the inflammatory lesions of peri-implantitis be carefully treated to improve the prognosis for the following dental treatments