The efficacy of 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (statins) for reducing cardiovascularevents has been established in large-scaled randomized controlled trials (RCT), and these trials have encompassedboth primary and secondary prevention. Also, the safety of statins has been confirmed. Therefore, the market forstatins is growing quite rapidly. Despite their proven benefits, a large number of patients who meet the guidelinecriteria for statin therapy are not receiving these drugs. Various strategies have been used to increase statin therapyin the target populations. However, the number of eligible patients taking statins has remained disappointing. It hasbeen suggested that over-the-counter availability of statins would allow more consumers to use statins and achievecardiovascular risk reduction. In contrast, those clinical trials have applied selection criteria to protect the internalvalidity at the expense of reducing the applicability of the trial’s findings to the wider population of patients seenin routine clinical practice. Consequently, patients who are prescribed statins in routine clinical practice may systematicallydiffer from those people who received statins in the clinical trials and may have different outcomes fromthose reported in the trials. This paper will review the efficacy of statins for preventing cardiovascular diseases, andsuggest the pitfalls of the randomized controlled trails and the problems in the prescription of statins in the realclinical practice. (Korean Circulation J 2006;36:77-83)