Transracial studies are a powerful tool for genetic association studies of multifactorial diseases, such as type 1 diabetes. We therefore studied the association of candidate genes, HLA, INS, CTLA4, PTPN22, and SUMO4, with type 1 diabetes in Asian populations in comparison with Caucasian populations. Class II HLA was strongly associated with type 1 diabetes in both Asian and Caucasian populations, but alleles associated with type 1 diabetes are different among different ethnic groups due to difference in allele distribution in general populations. INS was associated with type 1 diabetes in both Japanese and Caucasian populations, but frequency of disease-associated haplotype was markedly higher in Japanese than in Caucasian populations. CTLA4 association was reported for both type 1 diabetes and autoimmune thyroid diseases (AITD) in Caucasian populations, but the association with type 1 diabetes was concentrated in a subset of patients with AITD in Japanese. A variant (R620W) of PTPN22 was consistently associated with type 1 diabetes in Caucasian populations, but the variant was absent in Asian populations including Japanese. M55V variant of SUMO4 was significantly associated with type 1 diabetes in Asians, but genetic heterogeneity between Asian and Caucasian populations was suggested. These data indicate the importance of transracial studies with a large number of samples in each ethnic group in genetic dissection of type 1 diabetes.