Abstract : Background Improving outcomes of older patients admitted into intensive care units (ICU) is a raising concern. This study aimed at determining which geriatric and ICU parameters were associated with in-hospital and long-term mortality in this population. Methods : We conducted a prospective multicentric observational cohort study, including patients aged 75 years and older requiring mechanical ventilation, admitted between September 2012 and December 2013 into ICU of 13 French hospitals. Comprehensive geriatric assessment at ICU admission and ICU usual parameters were registered in a standardized manner. Survival was recorded and comprehensive geriatric assessment was updated after 1 year during a dedicated home visit. Results : 501 patients were analyzed. 108 patients (21.6%) died during the hospital stay. One-year survival rate was 53.8% (IC 95% [49.2%; 58.2%]). Factors associated with increased in-hospital mortality were higher acute illness severity score, resuscitated cardiac arrest as primary ICU diagnosis, perception of anxiety and low quality of life by the proxy, and living in a chronic care facility before ICU admission. Among patients alive at hospital discharge, factors associated with increased 1-year mortality in multivariate analysis were longer duration of mechanical ventilation, all primary ICU diagnoses other than septic shock, a Katz-activities of daily living (ADL) score below 5 and living in a chronic care facility before ICU admission. Among the 163 survivors at 1 year who received a second comprehensive geriatric assessment, the ADL score (functional abilities) showed a significant but moderate decline over time, whereas the Mini-Zarit score (family burden) improved. No significant change in patients’ place of life was observed after 1 year, and quality of life was reported as happy-to-very-happy in 88% of survivors. Conclusions : The mortality rate remains high among older ICU patients requiring mechanical ventilation. Factors associated with short- and long-term mortality combined geriatric and ICU criteria, which should be jointly evaluated in routine care. Clinical trial registration : NCT01679171