BACKGROUND: Kidney transplantation(KT) from unrelated donors has been increasing in Korea in recent years. However, the number of HLA antigen mismatches in unrelated donor KTis larger compare with that in related donor KT. Recently, some studies have reported that cross-reactive group(CREG) matching would improve graft outcome. METHODS: We studied a total of 277 cases of kidney transplants from unrelated donors(cadaver donor 195 cases, living unrelated donor 82 cases) in our center from March 1992 to August 1998. HLA class I antigens were assigned to 10 CREG antigens based on the amino acid residue system of Takemoto. HLA-DR antigens were assigned to 10 broad HLA antigens. Antigens present in donor but not in recipient were considered as mismatches. The survival analysis was carried out by Kaplan-Meier method and differences in survival rates were tested by log-rank test. RESULTS: Mean numbers of mismatches in HLA and CREGs were 4.0 and 2.9. Mismatched numbers of CREG-A,B and 5 year survival rates showed a linear association(P=0.01), but those of HLA-A,B did not show a linear association(P=0.88). Probability of finding zero or one CREG mismatched recipients in unrelated KT was 53%(146 cases). A significant statistic difference was noted in survival rates between zero or one and two or more CREG mismatched group(P=0.01). CONCLUSION: Zero or one CREG mismatched group had better survival in unrelated living or cadaveric KT. Applying CREG matching strategy to recipient selection, graft survival will be significantly improved in unrelated living or cadaveric KT.