The efficacy of treating hypercholesterolemia is often expressed in relative terms as the ratio of risk in treated vs untreated populations. However, the clinical impact of treatment is best measured by the difference in risk, which is called the attributable risk reduction. Attributable risk reduction is most useful clinically if it is reported for specific subgroups of patients according to age, sex, and other risk factors. To illustrate this concept, its applications and limitations, we review the literature on the primary and secondary treatment of hypercholesterolemia, present the attributable risk reduction, and describe its implications for clinical practice.