The 4S trial included 4 444 patients with angina pectoris or previous myocardial infarction and serum cholesterol 5.5-8.0 mmol/L on a lipid-lowering diet. They were randomised to double-blind treatment with simvastatin or placebo. During an average follow-up period of 5.4 years the incidence of nonfatal myocardial infarction decreased (relative risk 0.66, 95% CI 0.59 - 0.75, p < 0.00001) compared to a placebo, the need for coronary surgery decreased by 37% (p < 0.00001), and mortality in ischaemic heart disease decreased (relative risk 0.58, 95% CI 0.46 - 0.73). Total mortality decreased by 30%. The decrease was totally explained by the decrease in IHD mortality. The benefit of treatment was evident in both men and women, both in the young and in the elderly (aged 65 years or above), and the effect was not dependent on baseline cholesterol concentration.