Changes in the choroidal artery were examined at autopsy in 16 Japanese patients with hypertension and insulin-dependent diabetes mellitus. These changes could be divided into 1) arteriosclerotic ones consisting of intimal thickening due to migration of smooth muscle cells, 2) hyaline deposits in the subendothelium, 3) extensive degeneration (moth-eaten atrophy and necrosis) of medial smooth muscle cells, and 4) changes resulting from fibrinoplatelet thrombi and their organization (recanalization and obstruction). The intimal thickening and medial damage correlated with aging, were accelerated by hypertension, and were remarkable in arterioles less than 60 micron in diameter. Diabetes mellitus apparently did not enhance these vascular changes. Thrombotic occlusion or narrowing of the choroidal artery was frequently observed in the arterioles of patients with hypertension and diabetes mellitus who had chronic azotemia or renal insufficiency. Subendothelial hyaline deposits were increased in patients with diabetes. The narrowing or obstructive changes in the choroidal artery were extensive in the intraocular blood vessels. These changes may be secondary and induce damage to other intraocular blood vessels and tissues, including the retina.