The Heart Protection Study (HPS), with over 20,500 subjects, is the largest trial of statin therapy ever conducted. It provides important and definitive new information on women, the elderly, diabetics, and people with low baseline cholesterol pre-treatment and those with prior occlusive non-coronary vascular disease. It is a prospective double blind randomised controlled trial with a 2 x 2 factorial design investigating prolonged use (>5 years) of simvastatin 40 mg and a cocktail of antioxidant vitamins (650 mg vitamin E, 250 mg vitamin C and 20 mg beta-carotene). The HPS specifically included patients with high risk for coronary heart disease (CHD) but characteristics that excluded them from participation in previous statin trials. Simvastatin 40 mg treatment showed benefit across all patient groups regardless of age, gender or baseline cholesterol value and proved safe and well tolerated. Results show a 12% reduction in total mortality, a 17% reduction in vascular mortality, a 24% reduction in CHD events, a 27% reduction in all strokes and a 16% reduction in non-coronary revascularisations. Among high-risk patients in this western population (with a minimum total cholesterol [TC] > or = 3.5 mmol/l at entry) there appears to be no threshold cholesterol value below which statin therapy is not associated with benefit; even among those with pre-treatment cholesterol levels below current national recommended targets. Over the 5.5 year study period patients and their doctors were encouraged to add an active non-study statin to the study regimen if they wished to do so. Thus the trial eventually had only two-thirds complying with the original intention-to-treat design. Nevertheless, results were highly significant for the study statin--simvastatin 40 mg once daily. Preliminary results of the HPS are negative for the antioxidant vitamin cocktail but provide reassurance that vitamins do no harm.