BACKGROUND With higher life expectancy an increasing number of people with intellectual disability (PWID) are at risk for developing dementia. OBJECTIVE Since PWID are an often neglected patient population, the objective of this study was to investigate the prevalence of dementia in residential disability homes in Switzerland and to describe how residential homes organize dementia care. METHODS All residential homes for adults with disabilities in Switzerland (N = 437) were invited to participate in a cross-sectional survey. A subset of questions covered the number of residents with diagnosed and suspected dementia and the organization of dementia care. The response rate to the dementia-related questions was 32% (n = 140 care homes with 10403 residents). RESULTS In residential homes specialised in PWID, 5.8% of the residents were reported to have a diagnosed or suspected dementia. In 140 deaths of PWID, 26% (n = 37) died with a diagnosed or suspected dementia. Residential homes for PWID mostly rely on internal resources (67.7%), general practitioners (61.3%) or psychiatrists (45.2%) for the care of residents with dementia, while specialized dementia nurses are rarely involved (16.1%). CONCLUSION This is the first study in Switzerland to assess the prevalence of dementia in PWID. The study indicates a diagnostic gap. Dementia care is provided in a heterogeneous way across Swiss residential homes for people with disability. Since the number of PWID requiring such care will likely increase in the future, best-practice examples and guidelines are needed.