BACKGROUND: Patients who experience an acute coronary syndrome are at heightened risk of recurrent ischemic events, including stroke. Ezetimibe improved cardiovascular outcomes when added to statin therapy in patients stabilized after acute coronary syndrome. We investigated the efficacy of the addition of ezetimibe to simvastatin for the prevention of stroke and other adverse cardiovascular events in IMPROVE-IT (Improved Reduction of Outcomes: Vytorin Efficacy International Trial), with a focus on patients with a stroke before randomization. METHODS: Patients who experienced acute coronary syndrome were randomized to a placebo/simvastatin or ezetimibe/simvastatin regimen and followed for a median of 6 years. Treatment efficacy was assessed for the entire population and by subgroups for the first and total (first and subsequent) events for the end points of stroke of any etiology, stroke subtypes, and the primary trial end point at 7 years. RESULTS: Of 18 144 patients, 641 (3.5%) experienced at least 1 stroke; most were ischemic (527, 82%). Independent predictors of stroke included prior stroke, older age, atrial fibrillation, congestive heart failure, diabetes mellitus, myocardial infarction, and renal dysfunction. There was a nonsignificant reduction in the first event of stroke of any etiology (4.2% versus 4.8%; hazard ratio [HR], 0.86; 95% confidence interval [CI], 0.73-1.00; =0.052) with ezetimibe/simvastatin versus placebo/simvastatin, driven by a significant 21% reduction in ischemic stroke (3.4% versus 4.1%; HR, 0.79; 95% CI, 0.67-0.94; =0.008) and a nonsignificant increase in hemorrhagic stroke (0.8% versus 0.6%; HR, 1.38; 95% CI, 0.93-2.04; =0.11). Evaluating total events, including the first and all recurrent strokes, ezetimibe/simvastatin reduced stroke of any etiology (HR, 0.83; 95% CI, 0.70-0.98; =0.029) and ischemic stroke (HR, 0.76; 95% CI, 0.63-0.91; =0.003). Patients who had experienced a stroke prior to randomization were at a higher risk of recurrence and demonstrated an absolute risk reduction of 8.6% for stroke of any etiology (10.2% versus 18.8%; number needed to treat=12; HR, 0.60; 95% CI, 0.38-0.95; =0.030) and 7.6% for ischemic stroke (8.7% versus 16.3%; number needed to treat=13; HR, 0.52; 95% CI, 0.31-0.86; =0.011) with ezetimibe added to simvastatin therapy. CONCLUSIONS: The addition of ezetimibe to simvastatin in patients stabilized after acute coronary syndrome reduces the frequency of ischemic stroke, with a particularly large effect seen in patients with a prior stroke. CLINICAL TRIAL REGISTRATION: URL: https://www.clinicaltrials.gov. Unique identifier: NCT00202878.