Although risk-factor modification has gained wide acceptance as an effective approach to the prevention of coronary heart disease (CHD), health planners, physicians and patients confront considerable uncertainty over the most appropriate and efficient preventive strategies. Some preventive approaches are both inexpensive and effective; others are expensive while their effectiveness is slight or unproven. Effectiveness varies with an individual's age, gender and other risk factors. Information provided by a cost-effectiveness analysis can clarify the value of alternative strategies for CHD prevention in specific populations, thereby helping to choose among them. It does so by producing a standard measure of value--the cost per year of life saved (YLS) or cost per quality-adjusted life-year (QALY) saved--that reveals which of several alternative interventions provides the greatest health benefit from a given expenditure. This article summarises the extensive literature on the cost effectiveness of CHD prevention with an emphasis on primary prevention. Published work indicates that smoking-cessation programmes, particularly those that rely on counselling with or without nicotine supplements, are highly cost effective in many settings. Although the evidence is limited, exercise programmes also appear to be cost effective. The detection and treatment of hypertension is highly cost effective, particularly when inexpensive drugs with proven effectiveness, such as diuretics or beta-blockers, are used. Hormone-replacement therapy is a cost-effective approach to CHD prevention in most postmenopausal women, although direct clinical trial data are lacking and it is uncertain which hormone preparation is best. Cholesterol reduction is a cost-effective strategy for the prevention of CHD in individuals without other treatable risk factors who are at very high risk of developing CHD. For individuals with multiple CHD risk factors, the choice of risk-modification strategies is complex and depends upon the interactions of risk and the relative costs of treating each risk.