The objective is to define the clinical echocardiographic characteristics and cardiovascular outcome in patients with acute heart failure (HF) with versus without diabetes mellitus (DM). Demographic, clinical, laboratory, and echocardiographic data were collected in Olmsted County adults hospitalized for acute HF between 2005 and 2008. Analyses were performed for mortality and acute HF hospitalization outcomes stratified by diabetic status, systolic function, and diastolic function. There were 912 subjects who met inclusion criteria, and mean age was 79 (SD 13.1) years with 53% women. Prevalence of DM was 42% in the study population, and those with DM had worse diastolic function and increased mortality and HF rehospitalization. Among those with DM and acute HF, reduced left ventricular ejection fraction and worse diastolic function conferred increased HF rehospitalization (p = 0.010 and p = 0.022, respectively). In conclusion, DM is common in those hospitalized for acute HF and is associated with worse long-term clinical outcomes. The subgroup of DM with acute HF and left ventricular systolic dysfunction or diastolic dysfunction had worse HF rehospitalization outcomes.