OBJECTIVE: Diabetes mellitus is associated with an increased risk of cardiovascular disease (CVD) and death. Because the prevalence of diabetes is rising worldwide and chronic heart failure (CHF) is becoming increasingly common with the aging population, it is timely to examine the impact of diabetes per se on 1-year adverse outcomes in patients with CHF. RESEARCH DESIGN AND METHODS: We prospectively assessed whether diabetes status independently affected the 1-year risk of all-cause and CVD mortality and first hospitalization for worsening heart failure (HF) in a multinational cohort of 9,428 outpatients with CHF enrolled in the European Society of Cardiology and Heart Failure Association Long-Term Registry. RESULTS: Compared with those patientswithout diabetes, patientswith diabetes (n = 3,440, 36.5%) had higher cumulative rates of 1-year all-cause death (9.4% vs. 7.2%; adjusted hazard ratio [HR] 1.28; 95% CI 1.07-1.54), CVD death (4.8% vs. 3.8%; adjusted HR 1.28; 95% CI 0.99-1.66), and HF hospitalization (13.8% vs. 9.3%; adjusted HR 1.37; 95% CI 1.17-1.60), all independent of age, sex, BMI, smoking, systolic blood pressure, estimated glomerular filtration rate, hemoglobin, HF etiology, left ventricular ejection fraction, hypertension, statin use, and prior stroke or chronic obstructive pulmonary disease. Among CHF patients with HbA1c measurements available at baseline (n = 2,567), there was a significant and independent association between increasing HbA1c levels and the risk of 1-year survival outcomes. CONCLUSIONS: The presence of diabetes markedly increases the risk of 1-year adverse clinical outcomes in outpatients with CHF independent of multiple common risk factors. More effective and personalized treatment for diabetes should be considered in this particularly high-risk patient population.