There is evidence from epidemiology, pathophysiology, and clinical trials that high LDL cholesterol levels cause atherosclerotic heart disease. Current guidelines recommend an LDL cholesterol target of 70 mg/dL for patients at high or very high risk. The risk imposed by LDL cholesterol is modulated by the presence of additional risk factors such as age, smoking, and indices of inflammation. Epidemiologic studies as well as rare congenital conditions (e.g., hypobetalipoproteinemia) have shown that very low LDL cholesterol (lower than 70 mg/dL) levels are associated with a very low risk of cardiovascular disease. Analyses of randomized clinical trials have shown a greater benefit in reducing the risk of cardiovascular disease (without an increase in adverse events) among those with very low achieved LDL (below 40 mg/dL). In one study of patients with achieved LDL cholesterol below 30 mg/dL, there was no increase in the usual adverse events compared to patients with LDL cholesterol levels above 30 mg/dL. High-intensity statin therapy is associated with a higher rate of transaminase elevations, but no hepatic failure, a very small risk of myopathy, and an increased risk of developing diabetes. However, the small increase in the risk of developing diabetes is much smaller than the marked lowering of cardiovascular risk. The duration of statin therapy may be important in studies of primary prevention and early, probably low-dose statin therapy, may achieve primordial prevention of atherosclerotic disease.