BACKGROUND: This study analysed the cost of intensive home care packages for people with dementia living on the boundary of home care and residential care facilities in Ireland. The cost of community-based services and supports, including informal care and private out-of-pocket expenditure, was compared to the cost of public and private residential care. METHODS: The study recruited 42 people with dementia and/or their caregivers, who were living on the boundary of home care and residential care, to an in-depth study on the cost of care. The Resource Utilization in Dementia scale was used to collect data on the utilization of standard formal care and informal care by people with dementia in receipt of an intensive home care package. Information on private out-of-pocket expenditure on care was also collected. Unit costs were assigned and community-based care was compared with public and private residential care alternatives. RESULTS: The average weekly cost of home care, including the intensive home care package, standard formal community care provision, medications, consumption and housing, was estimated at €1127. This is lower than the average weekly cost of public long-stay care facilities (€1526) and around the same as for private nursing home fees in the Dublin region (€1149). When the opportunity cost valuation of informal care is included, the cost of home care is higher than all types of residential care. Adding private care expenditure further inflates the cost of home care. CONCLUSION: Keeping highly dependent people with dementia living at home is not cheap and raises questions about optimal resource allocation on the boundary of home care and residential care. Even with significant public spending on intensive home care packages, family care costs remain high. So too does private out-of-pocket expenditure on care for some people with dementia.