Behçet's disease has been shown to be strongly associated with the human leukocyte antigen (HLA) B51, not only in the Japanese but also in many other ethnic groups living in the area that extends from the Middle East to Japan. Specific antigen presentation by B51 molecules may be involved in the development of Behçet's disease. Furthermore, studies of the HLA-C genotype conducted using a polymerase chain reaction-sequence specific primers method have suggested that the gene involved in the pathogenesis of Behçet's disease is not the HLA-C gene but some other gene located near the HLA-B gene. Polymorphic analysis of the Tau-a microsatellite located between the HLA-B and TNF genes have also indicated that the Behçet's disease gene is located near the HLA-B gene but is not the HLA-B51 gene itself. We and others believe that many important genes exist in the region located between the TNF and HLA-B or HLA-C genes, including the MIC, PERB, and NOB genes. In this paper, we review current data on genetic factors involved in the development of Behçet's disease.