OBJECTIVE The aim of this retrospective study was to verify the stability of three types of short implants 8.5mm or less. BACKGROUND Techniques such as alveolar bone graft, sinus bone graft, inferior alveolar nerve repositioning are necessary to avoid damage of anatomical structures for the patient who has insufficient residual ridge. However it has been recently reported that short implant, which has improved surface, can lead to successful osseointegration as well as prosthetic treatment. MATERIALS AND METHODS Implants 8.5mm or less were placed by one surgeon. Initial stability and secondary stability, osseointegration failure, intraoperative and postoperative complications, complication of dental prosthesis, amount of the marginal bone resorption, and the success or survival rate of implant were retrospectively evaluated using medical record and radiographic analysis. RESULT For 48 patients(male:female=27:21), the average age was 50 years old. Among 70 short implants, 24 implants satisfied the inclusion criteria. All implants were placed in premolar or molar regions of the mandible. Relatively short-term stability were confirmed during healing period. ? measured by osstell mentor(75.67 ISQ) or periotest(-3.41 PTV) at 1st or 2nd operation. The mean secondary stability value was higher than primary stability value. 16 implants were restored with fixed partial prosthesis and 8 implants with single crown. The mean C/I ratio was 1.22 (S.D. 0.27 ; range= 0.64 to 1.67). The One-year after the loading, mean marginal bone loss was 0.18mm(S.D. 0.31) and no implant was lost. Complications were observed in 4 cases(16%); 1 case of screw-loosening, 3 cases of cover screw exposure. CONCLUSION In this study, short implants 8.5 mm or less showed relatively favorable short-term prognosis. Therefore short implant for the mandible with insufficient height of residual ridge is considered to be a good indication.