We reported the pathological findings of an autopsy case of thrombotic thrombocytopenic purpura, with special reference to the topography of vascular lesion in the central nervous system. Amorphous eosinophilic, PAS-positive thrombi, endothelial proliferation and aneurysmal dilatation of affected vessels were prominent features in the visceral organs such as the heart, kidneys, liver, pancreas, adrenals, thyroid and alimentary tracts. Most of these vascular lesions were restricted to the arteriolar-capillary junctions. There were no thrombi in the lungs as reported previously. In addition, the thrombi were rarely seen in so-called portal vessels existed in the liver, pancreas and anterior pituitary gland. In the central nervous system, there were many vascular lesions similar to those of visceral organs in the cerebral gray matter, brain stem and cerebellar cortex. A few lesions were also seen in the white matter, subarachnoid space and choroid plexus. Many foci of chromatolytic neurons as well as a few petechial hemorrhages and minute infarcts were observed in the parenchyma. The characteristic of the vascular lesions in the cerebral and cerebellar cortex was the sites of thrombi. They were predominantly located at the bifurcation of arterioles, 20-50 microns in diameter, and were numerous in the third or fourth cortical layer of the cerebrum, and in the Purkinje cell layer of the cerebellum. Although the etiology of TTP is still unknown, the characteristic topography of vascular lesions suggests primary endothelial involvement in this disease.