An analysis of randomized trials evaluating the effect of cholesterol reduction on total mortality and coronary heart disease incidence. The primary aim of this study was to estimate the relation between cholesterol reduction and total mortality and coronary heart disease (CHD) incidence. Secondarily, the clinical issues of whether the efficacy of cholesterol lowering is dependent on the treatment modality, presence of CHD at baseline, or the simultaneous introduction of other interventions was explored. All randomized clinical intervention trials of cholesterol reduction were used in an overview analysis of total mortality rate and CHD incidence; analysis was performed with weighted linear regression. The trials include those that used primary and secondary intervention, diet and drugs, and single or multifactor design. Nineteen trials were analyzed for total mortality, and of the 19, 16 were analyzed for CHD incidence rate. Net difference in cholesterol change between study groups was used as the independent variable, and the three previously mentioned dichotomous design characteristics were used as additional independent variables. For every 1% reduction in cholesterol, an estimated 2.5% reduction in CHD incidence is indicated (95% CL: 1.1, 3.9). With regard to CHD drug trials tended toward better efficiency in cholesterol lowering than did dietary trials. With regard to total mortality, this efficiency was higher in secondary than in primary preventive trials. The efficiency was also somewhat dependent on the baseline cholesterol level. This study shows that cholesterol reduction is effective in lowering CHD incidence, but cholesterol reduction must be at least 8-9% to be effective in lowering total mortality. 