Purpose The very old patients over 80 years with acute decompensated heart failure (ADHF) have been increasing rapidly, but their clinical characteristics and prognosis were not systemically evaluated. Method The Korean Acute Heart Failure (KorHF) Registry enrolled 3,200 patients with acute decompendsated heart failure from Nov 2005 to Nov 2009 in 24 university hospitals in South Korea. They were divided into three aged groups; ���80 (group 1; n=600, 84.6짹3.6 years), 65-79 (group 2; n=1,495, 72.5짹4.3 years), <65 years old (group 3; n=1,105, 51.7짹11.0 years). Results More patients in group 1 were women and non-smokers, and had co-morbid conditions such as previous HF, old myocardial infarction, or COPD. Ischemic heart disease was the main cause (44%) of ADHF. NYHA functional class and serum NT-proBNP was higher. Less patients in group 1 showed sinus rhythm (62.9%) in the initial ECG. Echocardiography showed smaller left ventricular (LV) chamber size and higher LVEF. Less patients in group 1 were taking beta-blockers (31.3% vs. 42.6% in group 2 and 44.4% in group 3, p<0.001) and spironolactone (24.3% vs. 31.6% in group 2 and 37.7% in group 3, p<0.001). Total duration of ICU and hospital stays, and in-hospital mortality were not significantly different among groups. 1-year mortality was highest of group 1 (20.4% vs. 14.6% in group 2 and 8.9% in group 3, p<0.001), but 1-year readmission rate due to ADHF of group 1 was not different (18.0% vs. 20.6% in group 2, 17.6% in group 3) Conclusions About one fifth of patients enrolled in KorHF Registry were over 80 years old. They showed high mortality and morbidity. Clinical trials and different therapeutic strategy may be required to improve their long-term prognosis.