In an observational study, we examined the effect of statins on low-density-lipoprotein (LDL) subfractions.Using density-gradient ultracentrifugation, we measured small, dense LDL density in 612 patients (mean age, 61.7 ± 12.6 yr), some with and some without coronary artery disease, who were placed in a statin-treated group (n=172) or a control group (n=440) and subdivided on the basis of coronary artery disease status.Total cholesterol, LDL cholesterol, apolipoprotein B, and the LDL cholesterol/apolipoprotein B ratio were significantly lower in the statin group. However, the proportion of small, dense LDL was higher in the statin group (42.9% ± 9.5% vs 41.3% ± 8.5%; P=0.046) and the proportion of large, buoyant LDL was lower (23.6% ± 7.5% vs 25.4% ± 7.9%; P=0.011). In the statin group, persons without coronary artery disease had higher proportions of small, dense LDL, and persons with coronary artery disease tended to have higher proportions of small, dense LDL.Our study suggests that statin therapy--whether or not recipients have coronary artery disease--does not decrease the proportion of small, dense LDL among total LDL particles, but in fact increases it, while predictably reducing total LDL cholesterol, absolute amounts of small, dense LDL, and absolute amounts of large, buoyant LDL. If and when our observation proves to be reproducible in subsequent large-scale studies, it should provide new insights into small, dense LDL and its actual role in atherogenesis or the progression of atherosclerosis.