Takayasu arteritis, Buerger's diseases, temporal arteritis, vascular Behcet disease and inflammatory abdominal aortic aneurysm are classified in Japan as intractable vasculitides involving mainly large vessels, because their etiologies are not yet elucidated and, therefore, treatments for them were not yet established. Recent experimental and vascular biological studies, however, have focussed on the roles of virus infection in vasa vasorum (vasa vasoritis) and on the subsequent inflammatory vascular changes through HLA and/or other autoimmune mechanisms. Several studies including ours have demonstrated that these vascular inflammatory changes progress from the adventitial side to the intimal side of the vessel, finally complicating atherosclerotic changes in the intima. These vascular inflammatory changes are also recognized during progression of atherosclerosis and these observations strongly suggest that inflammation is a serious risk factor of atherosclerosis.