Non-cardiac comorbidities are highly prevalent in patients with heart failure (HF). Our objective was to define the association between non-cardiac comorbidity burden and clinical outcomes, costs of care, and length of stay within a large randomized trial of acute HF patients. Patients with complete medical history for the following comorbidities were included: diabetes mellitus, chronic obstructive pulmonary disease, chronic liver disease, history of cancer within the last 5 years, chronic renal disease (baseline serum creatinine >3.0 mg/mL), current smoking, alcohol abuse, depression, anaemia, peripheral arterial disease, and cerebrovascular disease. Patients were classified by overall burden of non-cardiac comorbidities (0, 1, 2, 3, and 4+). Hierarchical generalized linear models were used to assess associations between comorbidity burden and 30-day all-cause death or HF hospitalization and 180-day all-cause death in addition to costs of care and length of stay. A total of 6945 patients were included in the final analysis. Mean comorbidity number was 2.2 (± 1.34). Patients with 4+ comorbidities had higher rates of 30-day all-cause death/HF hospitalization as compared with patients with no comorbidities [odds ratio (OR) 3.32, 95% confidence interval (CI) 1.61-6.84; P < 0.01]. Similar results were seen with respect to 180-day death (OR 2.13, 95% CI 1.33-3.43; P < 0.01). Higher comorbidity burden was associated with higher 180-day costs of care and length of stay. Higher comorbidity burden is associated with poor clinical outcomes, higher costs of care, and extended length of stay. Further studies are needed to define the impact of comorbidity management programmes on outcomes for HF patients.