The etiology of Takayasu's truncoarteritis is still unknown, although recent studies have suggested the participation of immunogenetic factors in the pathogenesis of this disease. Based on the summary of autopsy findings and taking clinical features into consideration, the current criteria for the pathological diagnosis of this condition might be summarized as follows. 1) Non-syphilitic truncoarteritis frequently occurring in young females. 2) Frequent manifestation of pulseless syndrome, and occasional presence of specific eye-ground findings or hypertension. 3) Common involvement of cranial stem arteries, and frequent involvement of the entire aorta and pulmonary artery. 4) Lesions in the stem arteries initially develop in the form of mesoperiarteritis by way of the vasa vasorum, and this is followed by intense intimal and adventitial fibrosis and occasionally thrombus formation. 5) Inflammatory changes in the media and adventitia exhibit histologically granulomatous inflammation with giant cells, diffuse productive inflammation consisting of lymphocyte and plasma cell infiltration, diffuse or nodular fibrosis accompanied by disintegration and loss of elastic fibers. 6) Marked fibrosis of the affected stem artery causes stenosis or obliteration of the lumen, and leads to aneurysm formation or dilatation of the artery.