The application of molecular biology and genetics in the field of cholesterol and lipoprotein metabolism has resulted in a tremendous expansion of knowledge during the past decade. In this short review, the normal metabolism of lipoproteins is first discussed briefly, and several clinically important examples of genetic disorders which have recently been characterized are discussed: hypobetalipoproteinaemia, familial defective apo B-100, type III hyperlipoproteinaemia, and familial hypercholesterolaemia. New data on the molecular regulation of cholesterol metabolism are summarized, and the impact of this knowledge for our future therapeutic possibilities in hypercholesterolaemia and certain malignant diseases is discussed.