Morphology of atheromatous plaques from human intracranial arteries was examined by light and electron microscopy. Overall morphology of lesions did not differ from those reported for other arterial beds. In the presence of an intact elastic membrane, lipid cores were localized only to the intima and covered with a fibromuscular cap. Lipid-filled cells at the periphery resembled smooth muscle cells or blood monocytes, but within the atheromatous core took the form of macrophages filled with lipid crystals and variable-density lipid droplets. Calcium crystallized spherules were localized to the surface of translucent lipid crystals which themselves were seen to coalesce with large amorphous lipid droplets. This study together with previous studies on cerebral arteries suggest that fatty streak lesions may undergo transformation to atheromatous plaques. Similarity in structure of atherosclerotic plaques between cerebral and other arterial beds suggests that documented differences in susceptibility to atheroma of various vascular beds in relation to age cannot be resolved by morphological studies alone.