["Journal of Intellectual Disability Research, EarlyView. ", "\nABSTRACT\n\nBackground\nAdults with intellectual disability (ID) experience frailty up to 20 years earlier than the general population, potentially increasing their risk of age‐related comorbidities and mortality at a younger age. This study investigates the relationship between frailty, assessed with the Intellectual Disability Frailty Index (ID‐FI) and its Short Form, and all‐cause mortality over 10 years in older adults with ID. Accurate mortality prediction may help identify high‐risk individuals and assist in creating targeted interventions for adults with ID.\n\n\nMethods\nData from 982 participants aged ≥ 50 years (mean age = 61.6 ± 8 years) with borderline to profound ID were analysed over a 10‐year follow‐up within the Healthy Ageing and Intellectual Disabilities (HA‐ID) cohort. Frailty was assessed using the 51‐item ID‐FI and the 17‐item ID‐FI Short Form, which measure frailty scores that can be classified into five categories: relatively fit, prefrail, mildly frail, moderately frail and severely frail. Cox proportional hazards models were used to assess the predictive validity of both indices for all‐cause mortality.\n\n\nResults\nOf 982 study participants, 433 (44.1%) were deceased during 10‐year follow‐up. Higher frailty scores were significantly associated with increased mortality risk, independent of age, sex, level of ID and Down syndrome. Compared to relatively fit participants, the hazard ratios (HRs) for mortality for the ID‐FI were as follows: 1.53 (95% CI = 1.14–2.05) for prefrail, 3.17 (95% CI = 2.31–4.36) for mildly frail, 5.37 (95% CI = 3.66–7.89) for moderately frail and 10.00 (95% CI = 6.49–15.43) for severely frail participants. A similar pattern was demonstrated for the ID‐FI Short Form. Both indices demonstrated fair predictive accuracy (AUC = 0.72) for 10‐year all‐cause mortality.\n\n\nConclusions\nBoth the ID‐FI and ID‐FI Short Form are predictive for 10‐year mortality risk in adults with ID. Future research should investigate how frailty changes over time and develop strategies to improve care for adults with ID.\n\n"]