["Journal of Applied Research in Intellectual Disabilities, Volume 39, Issue 3, May 2026. ", "\nABSTRACT\n\nBackground\nLonger life expectancy in Down syndrome (DS) has shifted concern to age‐related declines in everyday functioning. Adaptive and maladaptive behaviours are pivotal to quality of life, yet little is known about their patterns in older adults with DS.\n\n\nMethod\nData from 259 cognitively stable adults (25–72 year) in the Alzheimer's Biomarkers Consortium–DS were analysed. Adaptive behaviour (Vineland‐3) and maladaptive behaviour (Reiss Screen) were analysed and then regressed on age, intellectual disability level, and cognitive tests.\n\n\nResults\nHigher age and greater disability predicted poorer adaptive functioning, but effects waned after cognition was included. General cognition, cued‐recall memory, and inhibitory control independently predicted adaptive skills. Maladaptive behaviours were rare, lacked cognitive or demographic predictors, and correlated negatively with adaptive scores.\n\n\nConclusions\nBy identifying strengths, vulnerabilities, and predictors of behavioural functioning, this study offers insight into future clinical and caregiving strategies for aging adults with DS.\n\n"]