ObjectivesTo determine if age, previous functional status, or acute severity of illness affect the acute and long-term mortality rates and functional status of the very elderly (≥85 yrs) after an ICU admission.DesignCohort study (retrospective entry for the first year of the study and prospective entry thereafter with prospective follow-up throughout).SettingAn ICU in a community teaching hospital with follow-up at home or at a skilled nursing facility.PatientsAll (n = 105) patients ≥85 yrs admitted to the ICU over a 2-yr period.Main Outcome MeasuresICU, 30-day post-hospital discharge, and 1-yr mortality rates, activities of daily living scores, organ system failure score at the time of ICU admission.ResultsThe ICU, 30-day posthospital discharge, and the 1-yr mortality rates were 30%, 43%, and 64%, respectively. Mortality rates significantly increased between the ICU stay or 30 days posthospital discharge and 1-yr follow-up periods. Of those patients who lived up to 6 months after hospital discharge, 86% survived to 1 yr with little change in functional status from baseline. In the patients with ≥2 organ system failures, there were 88% 30-day posthospital discharge and 100% 1-yr mortality rates. Severity of illness, as measured by the number of organ system failures, was associated with increased ICU (odds ratio 3.38; 95% confidence interval, 1.51 to 7.60;p< .005) and 1 yr (odds ratio 5.76; 95% confidence interval, 2.49 to 13.29;p< .0001) mortality rates, while age within this group and preadmission functional status were not.ConclusionsWithin the very elderly population, acute severity of illness is the most significant predictor of mortality after an ICU admission. For most very elderly patients, surviving 1 yr after an ICU admission, there is little change in functional status.