Takayasu arteritis is a chronic vasculitis characterized by a clinical pulseless condition and is predominant in young female patients. Its loci is found mainly in Asian countries, and its etiology is still unknown. Our experiences of cases of twin sisters with Takayasu arteritis led us to suppose that hereditary factors participate in the pathophysiology of this disease. Population and family-incidence studies employing HLA analysis in Japan have focused on an complotype Aw24-DW52-C4A2-C4BQ0-Dw12 which was in disequilibrium with Takayasu arteritis. Clinical features and clinical courses were found to be intimately related to this complotype. Recent studies on HLA typing in other countries have also suggested the important roles of hereditary factors in this morbid condition and international collaborative studies on these hereditary factors are now under way.