Introduction: Individual comorbidities have been shown to adversely affect prognosis in heart failure (HF). However, our knowledge of multimorbidity in HF and understanding of its prognostic implications still remain incomplete. Objectives: We aimed to analyze the prevalence of multimorbidity in Polish HF patients and to investigate the quantitative and qualitative impact of comorbidity burden on 12-month outcomes in that population. Patients and methods: We retrospectively analyzed data of 1765 Polish patients with ambulatory or acute (requiring hospitalization) HF from 2 multicenter observational European Society of Cardiology registries: the ESC-HF Pilot Survey (2009–2010) and ESC-HF-LT Registry (2011–2013). Results: Arterial hypertension and coronary artery disease were the most prevalent comorbidities, similarly to the entire European cohort. The great majority of HF patients had more than 1 predefined comorbidity and the most frequent number of comorbidities was 3. Importantly, in almost half of the patients, 4 or more comorbidities were reported. The best accuracy for predicting the adjusted 12-month rate of all-cause death was ensured by the model including only anemia and kidney dysfunction. The model including 4 comorbidities—anemia, kidney dysfunction, diabetes, and coronary artery disease—provided best accuracy for predicting 12-month rate of composite all-cause death or HF hospitalization. Conclusions: Multimorbidity is highly prevalent in a real-world cohort of Polish HF patients and the quantitative burden of comorbidities is related to increased mortality. In such patients, the clinical profile characterized by pathophysiological continuum of diabetes, kidney dysfunction, and anemia is particularly associated with unfavorable outcomes.