Lipid lowering treatment with 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor (statins) may reduce morbidity and mortality in patients with stable ischaemic heart disease. In trials where a statin was used as secondary prevention after an acute coronary syndrome (ACS), the treatment was initiated 3-6 months after the event. A high rate of serious complications occurs in the unstable clinical state after an ACS, including myocardial infarction and death. The incidence rate of serious complications declines after 1 month and then gradually diminishes. It has not been determined whether initiation of treatment with a statin soon after an ACS reduces the occurrence of early coronary events. Statins have effects on the vessel wall other than the lipid lowering effect, and these may partly account for the benefit of statin therapy. Whether these mechanisms are associated with a prognostic effect soon after an ACS has not been clarified.