PURPOSE: We assessed the association between the premorbid functional status (PFS) and 1-year mortality and functional status of very old intensive care patients. METHODS: Using a nationwide quality registry, we retrieved data on patients treated in Finnish intensive care units (ICUs) during the period May 2012‒April 2013. Of 16,389 patients, 1827 (11.1%) were very old (aged 80 years or older). We defined a person with good functional status as someone independent in activities of daily living (ADL) and able to climb stairs without assistance; a person with poor functional status was defined as needing assistance for ADL or being unable to climb stairs. We adjusted for severity of illness and calculated the impact of PFS. RESULTS: Overall, hospital mortality was 21.3% and 1-year mortality was 38.2%. For emergency patients (73.5% of all), hospital mortality was 28% and 1-year mortality was 48%. The functional status at 1 year was comparable to the PFS in 78% of the survivors. PFS was poor for 43.3% of the patients. A poor PFS predicted an increased risk of in-hospital death, adjusted odds ratio (OR) 1.50 (95% confidence interval, 1.07-2.10), and of 1-year mortality, OR 2.18 (1.67-2.85). PFS data significantly improved the prediction of 1-year mortality. CONCLUSIONS: Of very old ICU patients, 62% were alive 1 year after ICU admission and 78% of the survivors had a functional status comparable to the premorbid situation. A poor PFS doubled the odds of death within a year. Knowledge of PFS improved the prediction of 1-year mortality.