BACKGROUND: Statins administered early in patients with acute coronary syndromes may lead to modest reductions in recurrent ischemic events. OBJECTIVE: To examine the association between previous and early in-hospital statin therapy and the presentation and outcomes of an acute coronary syndrome. DESIGN: Cohort study. SETTING: 94 hospitals in 14 countries participating in the Global Registry of Acute Coronary Events (GRACE). PATIENTS: 19,537 patients with an acute coronary syndrome who were enrolled from April 1999 to September 2002. MEASUREMENTS: Statin use before and after presentation with an acute coronary syndrome and associated rates of myocardial infarction, hospital complications, and hospital mortality. The composite end point included death, in-hospital myocardial infarction, and stroke. RESULTS: Patients who were already taking statins when they presented to the hospital were less likely to have ST-segment elevation (odds ratio [OR], 0.79 [95% CI, 0.71 to 0.88]) or myocardial infarction (OR, 0.78 [CI, 0.70 to 0.86]). Patients who continued to take statins in the hospital were less likely to experience complications or die than patients who never received statins (OR, 0.66 [CI, 0.56 to 0.77]). Patients not previously taking statins who began statin therapy in the hospital were less likely to die than patients who never received statin therapy (OR, 0.38 [CI, 0.30 to 0.48]). However, adjustment for the hospital of admission attenuated the association between initiation of statin therapy and the composite end point (OR, 0.84 [CI, 0.65 to 1.10]). LIMITATIONS: This observational study cannot exclude confounding by clinical and hospital factors. CONCLUSIONS: These data support the hypothesis that statin therapy can modulate early pathophysiologic processes in patients with acute coronary syndromes. A randomized trial of statin therapy in acute myocardial infarction is warranted.