In a previous report1attention was called to the fact that familial xanthomatosis is by no means a rare disorder. It has long been so regarded only because its two most striking external manifestations, xanthoma tuberosum and xanthoma tendinosum, are met with infrequently. It was also pointed out that a close relation exists between this hereditary disorder and atherosclerosis. The present study enlarges and completes our data dealing with xanthomatous families and links the results with those of a previous investigation,2in which patients with coronary artery disease were studied for evidence of disturbed lipid metabolism. FAMILIAL XANTHOMATOSIS Thirty-Five Families and Twenty-Nine Additional Persons with Xanthomatosis During the past few years in which we have searched patients for stigmas of xanthomatous disease, we have encountered 64 persons (index cases) with this hereditary disorder and have studied 137 members of the families of 35 of these patients. In the