Lowering the blood cholesterol level is a safe method to improve survival for primary and secondary prevention of coronary heart disease. However, there is no evidence for any effectiveness in Japanese. This study was designed to evaluate the effect of cholesterol lowering therapy with 3-hydroxy-3-methylglutaryl coenzyme A(HMG-CoA) reductase inhibitor on cardiac events(death and reinfarction) in Japanese patients after myocardial infarction. A total of 290 patients after myocardial infarction were studied retrospectively. The patients were divided into 2 groups with or without HMG-CoA reductase inhibitor therapy for lowering blood cholesterol levels. The cumulative cardiac events and percentage change of cholesterol levels[total cholesterol and low-density lipoprotein (LDL) cholesterol level] were compared between the 2 groups. HMG-CoA reductase inhibitor therapy lowered plasma cholesterol levels significantly (total cholesterol level--11 +/- 20%, LDL cholesterol level--23 +/- 26%) in patients with hypercholesterolemia, whereas there was no change(total cholesterol level 4.3 +/- 22%, LDL cholesterol level--7.2 +/- 24%) in patients without hypercholesterolemia. HMG-CoA reductase inhibitor therapy reduced cardiac events significantly compared in patients with hypercholesterolemia(p = 0.0008), but there was no benefit in patients without hypercholesterolemia. We suggest that treatment with HMG-CoA reductase inhibitor therapy for lowering cholesterol levels was effective for secondary prevention after myocardial infarction in Japanese patients with hypercholesterolemia.