INTRODUCTION: Due to the severe shortage of deceased-donor kidneys in Japan, ABO incompatible (ABOi) living-donor kidney transplantation (LKT) has been performed since the late 1980s. Recently, ABOi LKT has been performed in patients with various backgrounds such as unrelated combinations. We compared the results of ABOi unrelated LKT with those of ABOi related LKT. METHODS: Forty consecutive ABOi LKT recipients were included. Patients were divided into two groups: G1 (unrelated donors, n=29), G2 (related donors, n=11). Mean recipient/donor age were 57.1±7.4/56.7±8.2 years in G1 and 39.8±14.5/57.9±11.1 years in G2. Mean duration of dialysis was 54.0±58.2 months in G1 and 24.6±24.2 months in G2, respectively. We compared the difference in the patient and graft survivals, and complications, such as acute rejection, cytomegalovirus antigenemia, and surgical complications between the groups. All patients received desensitization with plasmapheresis until pre-transplant ABO IgG titers became <16. Thirteen patients of G1 and 5 patients of G2 received rituximab before transplantation and others underwent splenectomy at the time of transplantation. RESULTS: The patient/graft (death censored) survivals were 100%/100% at 1 and 3 years in G1, 100%/100% at 1 year and 91%/100% at 3 years in G2. Acute rejection occurred in 5 (17%) of G1 and 3 (27%) of G2. The incidence of cytomegalovirus antigenemia was 62% in G1 and 73% in G2. Surgical complications occurred 4 (14%) of G1 and 3 (27%) of G2. The serum creatinine levels at 1 and 3 years were 0.9±0.3 and 0.9±0.2mg/dl in G1, 1.2±0.3 and 1.0±0.2mg/dl in G2. CONCLUSION: The patient and graft survivals, graft function and complications after LKT were the same in both groups. Unrelated donor kidneys had no negative impacts on the outcome of ABOi LKT.