Purpose: To use the World Health Organisation's International Classification of Functioning to measure disability following critical illness using patient-reported outcomes. Methods: A prospective, multicentre cohort study conducted in five metropolitan intensive care units (ICU). Participants were adults who had been admitted to the ICU, received more than 24 h of mechanical ventilation and survived to hospital discharge. The primary outcome was measurement of disability using the World Health Organisation's Disability Assessment Schedule 2.0. The secondary outcomes included the limitation of activities and changes to health-related quality of life comparing survivors with and without disability at 6 months after ICU. Results: We followed 262 patients to 6 months, with a mean age of 59 +/- 16 years, and of whom 175 (67%) were men. Moderate or severe disability was reported in 65 of 262 (25%). Predictors of disability included a history of anxiety/depression [odds ratio (OR) 1.65 (95% confidence interval (CI) 1.22, 2.23), P = 0.001]; being separated or divorced [OR 2.87 (CI 1.35, 6.08), P = 0.006]; increased duration of mechanical ventilation [OR 1.04 (CI 1.01, 1.08), P = 0.03 per day]; and not being discharged to home from the acute hospital [OR 1.96 (CI 1.01, 3.70) P = 0.04]. Moderate or severe disability at 6 months was associated with limitation in activities, e.g. not returning to work or studies due to health (P < 0.002), and reduced health-related quality of life (P < 0.001). Conclusion: Disability measured using patient-reported outcomes was prevalent at 6 months after critical illness in survivors and was associated with reduced health-related quality of life. Predictors of moderate or severe disability included a prior history of anxiety or depression, separation or divorce and a longer duration of mechanical ventilation. Trial registration: NCT02225938.