Familial hypercholesterolemia is a prototype for a class of diseases that result from defects in receptor molecules. The three cardinal features of familial hypercholesterolemia are: 1) a selective elevation in the plasma level of one cholesterol-carrying lipoprotein, low density lipoprotein (LDL); 2) a selective deposition of LDL-derived cholesterol in macrophage-like scavenger cells throughout the body, but not in parenchymal cells; and 3) inheritance as an autosomal dominant trait with gene dosage effect, i.e., the disease is more serious in patients with the homozygous than with the heterozygous state. In this article, we review the evidence that each of these cardinal features of familial hypercholesterolemia can be explained by a genetic defect in a cell surface receptor for plasma LDL.