The effect of statin therapy on subclasses of LDL, VLDL and HDL lipoproteins is unclear. We compared changes in serum lipids, apolipoproteins and nuclear magnetic resonance (NMR) spectroscopy measured lipoprotein subclass concentration and average particle size over a minimum 6 months treatment period of atorvastatin 10 mg vs. placebo in 122 men and women. All subjects had type 2 diabetes and a modest dyslipidaemia (mean LDL-cholesterol 3.2 mmol/l and median triglycerides 1.8 mmol/l) and had a previous myocardial infarction. Compared with placebo, atorvastatin therapy was associated with a greater decrease in medium VLDL (median within person change -13.4 vs. -5.9 nmol/l, P<0.001 adjusted for baseline level), small VLDL (median change -17.8 vs. -8.1 nmol/l, P=0.002), large LDL (mean within person change -167.9 vs. -48.6 nmol/l, P<0.001) and medium LDL (median within person change -101.8 vs. -22.3 nmol/l, P=0.017). Atorvastatin therapy was also associated with a greater increase in large HDL than placebo (median change 1.40 vs. 0.80 µmol/l, P=0.02) and there was little change in small HDL so that average HDL particle size increased significantly with atorvastatin (P=0.04). In addition to reducing levels of (enzymatically measured) triglyceride, LDL-cholesterol and apolipoprotein B in diabetic patients,atorvastatin significantly reduces NMR measured medium and small VLDL and large and medium LDL, and increases large HDL.