The Asymptomatic Carotid Artery Progression Study (ACAPS) compared the usefulness of lovastatin alone or in combination with warfarin in the prevention of 3-year progression of mean maximum intimal-medial thickness (IMT), which is a measure of early atherosclerosis. The factorally designed, placebo-controlled study enrolled 919 men and women aged 40–79 who had moderately elevated low-density-lipoprotein (LDL) cholesterol and a single maximum IMT of 1.5–3.5 mm in the carotid arteries. Lovastatin significantly reduced LDL cholesterol. The mean maximum IMT declined at an annual rate of 0.009 mm among those persons taking lovastatin while the mean maximum IMT increased by 0.006 mm in the controls (p = 0.001). In addition, deaths and the combined frequency of coronary deaths, nonfatal myocardial infarctions and strokes were significantly lowered among the lovastatin-treated groups. Only 5 strokes (3 hemorrhages) were detected in the study; all occurred among those persons who were receiving lovastatin placebo. Our study suggests that early administration of lipid-lowering drugs halts the progression of early atherosclerosis in the carotid artery. In turn, such early primary preventive treatment may lessen the risk of important ischemic vascular events including stroke.