Background: The population of older adults with intellectual disabilities is growing, creating new challenges for individuals, families and service providers. Although there has been increased research into the ageing process for adults with intellectual disabilities, there is little focused research investigating physical mobility. Materials and Methods: A proxy-response telephone survey was conducted to establish the prevalence and severity of mobility limitations among adults with intellectual disabilities, aged 45 years and over, using validated instruments to quantify mobility in a representative population-based sample. Results: Surveys were completed for 128 people. Mobility limitations were common, but the prevalence varied depending on the definition of mobility limitation. The prevalence of limitations was greater among females than males, but no clear age trend was seen. Conclusions: The common nature of mobility limitations among the growing population of older adults with intellectual disabilities has implications for service providers and policy-makers.