Aims Type 1 diabetes mellitus patients with microalbuminuria have endothelial dysfunction associated with the degree of albuminuria but not with LDL-cholesterol levels. Lipid-lowering agents such as statins may still be of benefit as they can correct endothelial dysfunction by both lipid and non-lipid mechanisms. We therefore examined the effects of atorvastatin on brachial artery endothelial dysfunction in these patients.Methods In a double-blind, randomized crossover study, 16 Type 1 diabetes mellitus patients with microalbuminuria received 6 weeks of atorvastatin 40 mg/day or placebo, separated by a 4-week washout. Brachial artery, endothelium-dependent, flow-mediated dilatation (FMD) and endothelium-independent, glyceryl trinitrate-mediated dilatation (GTNMD) were measured.Results Compared with placebo, atorvastatin produced a significant decrease in apolipoprotein B (34.2%), LDL-cholesterol (44.1%) (all P < 0.001), and oxidized-LDL (35.7%, P = 0.03). There was a non-significant increase in plasma cGMP (P = 0.13) on atorvastatin. FMD and GTNMD increased significantly on atorvastatin (FMD: atorvastatin +1.8 +/- 0.4%; placebo +0.2 +/- 0.4%, P = 0.007); (GTNMD: atorvastatin +1.3 +/- 0.9%; placebo -1.2 +/- 0.6%, P = 0.04). An increase in cGMP was independently correlated with an increase in FMD on atorvastatin (adjusted R-2 0.41, P = 0.02).Conclusion Atorvastatin improves endothelium-dependent and independent vasodilator function of the brachial artery in Type 1 diabetes mellitus patients with microalbuminuria. This may relate to pleiotropic effects of statins, in particular reduced oxidative stress and increased availability of nitric oxide.