Daily living skills are important to ageing adults with intellectual disabilities (ID). The purpose of this study was to investigate the level of these skills in older adults with ID and to investigate the influence of gender, age, level of ID and mobility on these skills. Daily living skills were measured with the Barthel Index (for Activities of Daily Living, ADL) and the Lawton IADL scale (for Instrumental Activities of Daily Living, IADL) in 989 adults with ID aged 50 years and over living in community-based and institutional settings. Descriptives were presented by categories of gender, age, level of ID and mobility. Regression analysis was used to investigate the influence of these variables on total and item scores of ADL and IADL questionnaires. ADL and IADL scores in older adults with ID are comparable to those of vulnerable patient groups. Total ADL score was mainly determined by mobility, while total IADL score was mainly determined by level of ID. Of all 18 separate items of these questionnaires, 11 were determined more by mobility than level of ID. The Barthel Index and Lawton IADL scale are recommended for future use in research and clinical practice in this group. This study stresses the need to support mobility older adults with ID as much as possible, in order to optimalize independency in this group. (Contains 3 tables.)