Takayasu arteritis is a primary inflammatory disease of elastic arteries such as the aorta, its larger branches and the pulmonary artery trunk. According to our recent statistical survey of autopsy cases in Japan, the frequency of the disease in all autopsy cases was approximately 0.033% and the sex ratio was 1:4.5. The most frequent ages of the onset were 20-30 years, those of the death were 40-50 years. The latter was delayed about 20 years in comparison with a previous report. In the recent cases, the vascular lesions widely expanded. Luminal dilatation and aneurysm formation also increased in frequency, their ratio being approximately 57%. In the autopsy cases, the following active lesions were observed: (1) acute exudative inflammation (including suppuration), (2) chronic non-specific productive inflammation and (3) various types of granulomatous inflammation. These findings suggest that many triggers may play a role in the morphogenesis of Takayasu arteritis. The inflammatory lesions are produced in the media and adventitia through the vasa vasorum, and terminate in a diffuse or nodular fibrosis. New active lesions are often observed near the old fibrotic ones. This suggests that Takayasu arteritis may be a progressive disease. Intimal thickening of the peripheral branches from the affected arteries is very often observed. In consequence, secondary ischemic lesions are formed in various organs, especially the heart, brain and kidneys.