The purpose of the present study lied in examining the incidence, treatment and failure causes of peri-implantitis by analyzing medical charts of those patients who underwent implant placement for the past 2 years. The subjects included those patients who underwent implant placement at the present hospital from January 2001 to December 2002. 3i implants were used for the analysis for the comparison of significance. A total of 301 patients were examined, among whom 102 were females and 199, males. Implants were placed in a total of 578 cases. The number of peri-implantitis was present in a total of 29 cases (21 males and 8 females), giving the incidence at 9.6%. The evidence of peri-implantitis was seen in 60 cases, which was in 10.4% of the patients. Among those cases with peri-implantitis, 28 cases (47%) underwent bone graft and 22 cases (43%) underwent maxillary sinus lift. Furthermore, 4 of these patients had systemic diseases such as diabetes or hypertension. Regular management is important for the prevention of peri-implantitis. In other words, early prevention through regular follow-ups to check the status of surrounding soft tissue would be needed to maintain implants.