To facilitate a discussion of the surrounding ethical issues, we retrospectively analyzed clinical backgrounds and prognoses in patients aged 80 years or older receiving mechanical ventilation. The mean age of the patients was 85.5±5.1 years, with a maximum of 103 years. The hospital mortality rate was 37.2%. By Kaplan-Meyer analysis, the median overall survival time of the patients was 86 days, and the 1-year survival rate was 32.5%. The patients aged 86 years or older had significantly shorter median survival time than those aged from 80 to 85 years (63 vs. 203 days, p<0.05). The median survival time of 37 hospital survivors after discharge was 431 days, and the 1-year survival rate was 53.5%. In total, 5 patients were admitted for further mechanical ventilation with the median event-free survival time without death or further mechanical ventilation being 352 days. At the time of discharge, 10 patients refused mechanical ventilation in the future. Furthermore, 16 of the 20 postdischarge patients who died received no mechanical ventilation. Although a long-term survival was obtained in some cases, prognosis was poor, especially in patients aged 86 years or older. Moreover, a significant number of patients wanted no further mechanical ventilation. We should examine these facts when considering mechanical ventilation in very old patients.