Background: The purpose of this study was to report the prevalence and the significance of clinically recognized chronic obstructive pulmonary disease (COPD) during acute coronary syndrome (ACS). Hypothesis: COPD in patients with ACS is associated with worse outcome. Methods: Data were derived from a prospective, multicenter, multinationalstudy of 8167 consecutive patients hospitalized with ACS from February to June 2007 in 6 Middle Eastern countries. Data were analyzed according to the presence or absence of COPD. Demographic, management, and in-hospital outcomes were compared. Results: The prevalence of COPD was 5.3%. When compared with non-COPD patients, COPD patients were older and more likely to have diabetes, hypertension, and dyslipidemia. Atypical presentations were more common in COPD patients (P = 0.001). COPD patients were less likely to be treated with thrombolytic therapy (P = 0.001), β-blockers (P = 0.001), and glycoprotein IIb/IIIa inhibitors, and more likely to receive angiotensin-converting enzyme (ACE) inhibitors. Although there was no difference in in-hospital mortality between the 2 groups, patients with COPD were more likely to have heart failure (P = 0.001). Despite the fact that COPD patients with ST-segment elevation myocardial infarction were less likely to receive thrombolytic therapy, they suffered more bleeding complications (2.8% vs 1%, P = 0.04), resulting in prolonged hospitalization. COPD was not an independent predictor of increased in-hospital mortality. Conclusions: In this large cohort of patients with ACS, the prevalence of COPD was 5·3%. Atypical presentation is common among COPD patients, and this may result in delayed therapy. ACS in COPD patients was associated with higher risk of heart failure and major bleeding complications without increased risk of in-hospital mortality.