Behcet's disease occurs most frequently among the Japanese and Mediterranean populations. This disease was shown to have a close association with HLA‐Bw51, a split antigen of HLA‐B5. Frequency of this antigen is highest in the male complete type, and lowest in the female incomplete type. Most patients inherited the HLA‐B5 from their mothers, and not from the fathers. The frequency of HLA‐B5 is equally high in populations with a high incidence of Behcet's disease, and it is possible that the susceptibility genes to Behcet's disease have been spread by the old nomadic tribes or by the Turks via the Silk Route.