Uncontrolled studies have shown that statins can improve cerebral vasoreactivity (CVR) in patients with mild small vessel disease. We sought to determine whether high-dose atorvastatin increases CVR compared with placebo in patients with severe small vessel disease. Ninety-four adults with recent lacunar stroke were randomly allocated in a double-blind manner to 80 mg of atorvastatin daily or matching placebo after stratification for hypertensive and diabetic status. The primary end point was change in CVR after 3 months of treatment. Secondary outcomes were changes in brachial and carotid artery endothelial-dependent vasodilations. At baseline, all patients had a severely impaired CVR (mean, 12.1%; 95% CI, 9.5-14.7) and carotid (mean, -0.25%; 95% CI, -1.17-0.67) and brachial artery (mean, 2.72%; 95% CI, 1.39-4.05) endothelial function. Despite reductions of 55% in low-density lipoprotein cholesterol and of 30% in high-sensitivity C-reactive protein in the active arm compared to placebo, atorvastatin 80 mg per day did not improve CVR or endothelial dysfunction of carotid and brachial arteries. We found no positive effect of 3-month treatment with atorvastatin on severe cerebral microvasculature endothelial dysfunction in patients with lacunar stroke.