Among patients admitted for acute decompensated heart failure (ADHF), half are aged 75 years or over. The high prevalence of co-morbidities and functional impairments in this age group may affect patient outcomes. To assess the association between co-morbidities, functional status and in-hospital mortality in patients with ADHF aged ≥75 years. A prospective, multicentre cohort study. Five French hospitals. Five hundred and fifty-five patients aged ≥75 years admitted to the emergency department with ADHF. Baseline clinical data and co-morbidities were recorded at admission. Functional status and cognition were assessed using the Katz index and Mini-Mental Status Examination score, respectively. The primary outcome was in-hospital mortality. We found high prevalences of co-morbidities and functional impairments including hypertension (74.0%), atrial fibrillation (40.2%), prior acute coronary syndrome (32.3%) and diabetes (18.2%). The average creatinine clearance was 56.3 ml/min/1.73 m(2) (interquartile range, 39.2-77.0). In-hospital mortality was 67/555 (12.1%; 95% confidence interval, 9.4-14.8). In multivariate analysis, in-hospital mortality showed a statistically positive association with prior loss of self-sufficiency (Odds ratio [OR]: 5.85 [2.25-12.19]), hyperglycaemia (OR: 1.80 [1.26-2.54] per 1 SD increase), prior cerebral ischaemic event (OR: 3.56 [1.51-8.44]) and troponin I elevation above upper limit of normal (OR: 2.81 [1.37-5.77]). In addition, systolic blood pressure (OR: 0.98 [0.97-0.99] per 1 mmHg increase) and creatinine clearance (OR: 0.72 [0.51-1.00] per 1 SD increase) were negatively associated with in-hospital mortality. Co-morbidities and functional impairments are associated with a worse short-term prognosis in patients aged ≥75 years admitted for ADHF. Assessing these parameters at admission may improve patient management.