Assistance with daily activities is crucial for persons living with dementia and disabilities, yet many face significant challenges in accessing adequate care and support. Using harmonized longitudinal survey data (2012-2018) from the United States, England, 18 European countries and Israel, and China, we found that at least one-fifth of persons with dementia and disabilities received no personal assistance for basic or instrumental activities of daily living (ADL/IADL), regardless of regional development level. Care gaps were widespread across both ADL and IADL limitations, as well as for informal and formal care. Disparities were evident, with less-educated individuals more likely to lack formal care, while those living alone often lacked informal support, resulting in the absence of any care. Alarmingly, care availability showed no improvement over time. Our findings underscore the urgent need for policies to address inequities and ensure critical access to care services for this vulnerable population worldwide.