Background Because many Japanese patients with hypercholesterolemia have received statin therapy for nearly a decade, there was a need to investigate the benefit of long-term treatment. The Japan Lipid Intervention Trial (J-LIT) Extension 10 study was planned to continue the original J-LIT study for a total of 10 years. Methods and Results All 51,321 patients (including 19,905 who agreed to continue the study) were analyzed. Low-dose treatment with simvastatin (mainly 5 mg/day) was continued throughout the study period and serum lipid levels were well controlled over 10 years. Incidence of adverse drug reactions during the 4-year extension period was lower than previously. Serum total cholesterol, low-density lipoprotein-cholesterol (LDL-C), and triglyceride levels showed a positive correlation with the risk of coronary events, whereas high-density lipoprotein-cholesterol showed an inverse correlation. Patients with an LDL-C level ≥140 mg/dl had a far higher risk of coronary events than those with a level <100 mg/dl. Conclusions Long-term, low-dose simvastatin therapy was safe and effective in Japanese patients with hypercholesterolemia. Serum LDL-C levels should be <140 mg/dl to decrease coronary risk and a low cholesterol level should be maintained for as long as possible. (Circ J 2008; 72: 1218 - 1224)