Seven cases of cavernous hemangioma of the liver found accidentally at autopsy were studied by electron microscope. The structures of the hemangioma consisted of capillaries and the intervening stromal cells. The endothelial cells contained pinocytotic vesicles, scattered ribosomes, rough endoplasmic reticulum, and Golgi apparatus. A distinct basement membrane was present beneath the endothelial cells, and multilaminated arrangement of the basement membrane was sometimes observed beneath the endothelial cells. The endothelial cells also contained numerous cytoplasmic filaments, but contained sparse specific endothelial granules. The internal elastic lamina was hardly seen at all in the hemangioma. The stromal cells showed typical smooth muscle cells, modified smooth muscle cells, and fibroblast-like cells. Elastic tissue as well as collagen fibers was present within the intervening stroma. Neither adventitia nor nerve fibers were found in the cavernous hemangioma. It is thought that cavernous hemangioma of the liver may be of a hamartomatous nature.