Background: The Actiwatch is increasingly being used to investigate sleep. The aim of this study was to investigate which sensitivity setting of the Actiwatch is most suitable to detect sleep disturbance in older adults with intellectual disability (ID). Method ;Two Actiwatch types were compared to polysomnography (PSG) in 10 older adults with mild ID, using a 1-min epoch-to-epoch comparison. Outcome measures were sleep detection percentage, wake detection percentage, and overall accuracy of both Actiwatches, and several sleep parameters. Results: The high sensitivity setting of the Actiwatch appeared most suitable to detect sleep disturbance in older adults with ID (wake detection percentage = 54.6%, sleep detection percentage = 89.7%). Sleep parameters calculated using the high sensitivity setting corresponded well to PSG outcomes. Outcomes were similar for both Actiwatches. Conclusions: We recommend using the high sensitivity setting of the Actiwatch for clinical evaluation of sleep, and for epidemiological research in older adults with ID.