Purpose : The aim of this study was to evaluate the survival rate of sintered porous-surfaced implants placed in the edentulous posterior mandibles, in relation to implant length and diameter, crown-to-implant ratio, and types of prostheses, for a maximum of eight years of functioning. Material and Methods : The study group consisted of 43 partially edentulous patients who visited Catholic University Hospital of Daegu and one private dental clinic. A total of 122 sintered porous-surfaced implants n $Endopore^{(R)}$ (Inn ova Life Sciences, Toronto, Ontario, Canada) -- were placed in the edentulous posterior mandibles, Two diameter sizes (4.1 mm and 5.0 mm) and four lengths (5.0 mm, 7.0 mm, 9.0 mm, and 12.0 mm) were used. One hundred and three implants were splinted and 21 implants were nonsplinted. The survival rates of the implants in relation to length, diameter, crown-to-implant ratio, and types of prostheses were investigated. Statistical data were analyzed using SPSS Win.Ver 14.0 software with the Chi-square test. Results : The survival rate of the 4.1mm diameter implants was 100% and 91.2% for the 5.0mm diameter implants. The survival rates of the implants of differing diameters were found to be statistically different (p=0.005). The survival rates of both the 5.0mm and 7.0 mm length implants were 100%. The survival rate of the 9.0mm length implants was 97.9% and for the 12.0mm length implants was 95.1%. There was no statistical difference in survival rates for the differing lengths of implants. Of the 103 prostheses that were splinted, the survival rate was 98.0%. The survival rate of splinted prostheses was higher than that of the non-splinted prostheses, but was found to be not statistically different. There were no failed cases when the crown-to-implant ratio was under 1.0. When the crown-to-implant ratio was between 1.0 and 1.5, the failure rate of the implants was 6.7%. No failure was recorded with the ratio range of 1.5 to 2.0. Relative to the crown-to-implant ratio of 1.0, the failure rates were statistically different (p=0.048). Discussion and Conclusion : The cumulative survival rate of the porous-surfaced implants placed in the edentulous posterior mandibles was 97.5%. Short porous-surfaced implants showed satisfactory results after a maximum of nine years of functioning in the edentulous posterior mandibles.