Acute rejection after renal transplantation is still the most common cause of graft failure during the early post-transplant period. To determine whether an acute rejection episode adversely affects long-term graft survival, we retrospectively analyzed our single center patients population of 1266 consecutive living donor kidney transplantations performed between April 1984 and October 1995. Five hundred twenty three recipients(41.3%) experienced 711 acute rejection episodes. Among these 711 episodes, 92.6% were respond to anti-rejection therapy and treatment failure rate was 7.6%. Late onset acute rejection, which developed 1 year after transplantation, showed poor treatment response(79.7%). There was statistically significant difference of graft survival rate between acute rejection free group and acute rejection group. Furthermore, the frequency of acute rejection, response rate the steroid pulse therapy and the degree f remission affected the graft survival rate. Donor source impacted on the development of acute rejection-33.1% in living related donor, 39.9% in living unrelated donor and 57.1% in cadaveric donor transplantation. In living related donor kidney transplantations, HLA identical pairs(11%) showed less acute rejection episodes than HLA haplo-identical pairs(38.7%). In living unrelated donor kidney transplantations, HLA antigen match adversely affected the acute rejection rate-43.9%, 35.8% and 30.6% in 1 ∼2, 3 and 4~5 Ag match group, respectively. ABO blood group compatibility, recipient` s age and compatibility of HLA DR Ag did not influenced to the development of acute rejection. These results suggest that the acute rejection could be a major determinant of long-term graft outcome.