Decreased levels of high density lipoprotein (HDL)-cholesterol are found in patients with hypertriglyceridaemia and in patients who have inherited disorders associated with premature coronary heart disease. Hereditary conditions associated with low levels of HDL-cholesterol and normal total cholesterol levels include familial hypoalphalipoproteinaemia, Tangier disease, fish eye disease, and lecithin: cholesterol acyltransferase deficiency. Secondary causes of low HDL-cholesterol levels include any condition that affects liver metabolism. A recent study of patients with coronary artery disease (CAD) who had normal levels of low density lipoprotein cholesterol and total cholesterol revealed that two-thirds of the men and four-fifths of the women had low HDL-cholesterol levels, suggesting that low HDL-cholesterol may be more prevalent than previously suspected. The high incidence of isolated hypoalphalipoproteinaemia in this group indicates that HDL-cholesterol measurements should be performed on all patients with CAD, regardless of their total cholesterol levels.