The prevention and treatment of coronary heart disease (CHD) necessitates vigorous dietary intervention so as to lower the serum cholesterol level by at least 6%. Greater decreases in serum cholesterol can bring about reversal of atherosclerosis. The critical dietary change is the reduction in intake of saturated fat and cholesterol. Some of this fat may be replaced by unsaturated fats, especially monounsaturated fat (olive or canola oil). Fish and the omega-3 fats they contain may also be useful for the prevention of CHD. The benefits of omega-3 fats occur within a few months and probably involve an anti-thrombotic effect. There is evidence that the intake of trans-fatty acids formed by the hydrogenation of oils should be reduced as they are associated with CHD. Hypolipidaemic drugs may be useful for persons at very high risk of CHD but should generally be avoided for primary prevention.