It is now clear that the various hyperlipidemias represent a heterogenous group of disorders, each having various clinical and laboratory characteristics, prognosis and treatment. The three disorders commonly associated with premature atherosclerotic vascular disease are Type II (hyperbetalipoproteinemia), Type III ("broad beta" or "floating beta" disease) and Type IV (hyperprebetalipoproteinemia or, endogenous hypertriglyceridemia). The diagnosis of each of these three disorders can be suggested by the fasting serum cholesterol level and the appearance of the fasting serum after it has remained overnight in a refrigerator. Type II disease is characterized by a clear serum and a pronounced to moderate hypercholesterolemia. It is treated by reducing dietary cholesterol and saturated fats, increasing dietary polyunsaturated fats, and cholestyrmine. Type IV disease is characterized by a turbid serum indicating hypertriglyceridemia and a normal or only slightly elevated serum cholesterol level. It is treated with weight reduction, a low carbohydrate diet and clofibrate. Type III disease is characterized by both a turbid serum and increased cholesterol levels. It is treated with weight reduction, a low cholesterol diet and clofibrate. With the treatment of all disorders the lipid values should improve; however, with the treatment of Type III disorder both triglyceride and cholesterol levels return to normal, xanthoma resorb and there is an improvement in the peripheral blood flow, indicating that there has been amelioration of the atherosclerotic process.