Background: People with intellectual disabilities are increasingly reaching older adulthood. Little is known about age-related change in the prevalence of challenging behaviours among older adults with intellectual disabilities. Materials and method: The frequency and severity of staff-averse challenging behaviours of 132 older adults with intellectual disabilities was assessed through informant ratings on the Inventory of Client and Agency Planning at two time points 8-10 years apart. Results: There was an intraindividual decline in the frequency and severity of challenging behaviour using both lenient and more restricted definitions of challenging behaviour. There was a low prevalence but high comorbidity of severe challenging behaviour. Level of mental retardation and adaptive behaviour were related to the frequency and severity of challenging behaviour. Conclusions: An understanding of age-related intraindividual change in challenging behaviour has implications for staff wellbeing and optimizing the care of older adults with intellectual disabilities.