BACKGROUND: Dementia presents a significant challenge to health systems and to the person and family affected. Home care is increasingly seen as a key service in addressing this challenge in a person-centred and cost-effective way. Intensive Home Care Packages (IHCPs) were introduced in Ireland to provide personalised and high levels of support for people with dementia to remain at home or be discharged home from hospital, and to build on the work of the HSE & Genio Dementia Programme. This realist evaluation is concerned with real world questions of feasibility and effectiveness; specifically understanding in what ways IHCPs work, how optimum outcomes are achieved, for whom and in what contexts do IHCPs work best. METHODS: A mixed-method, multi-stakeholder study was designed within a realist evaluation conceptual framework. The process evaluation includes semi-structured interviews with health service staff at all levels, social network analysis and secondary database analysis; the outcomes evaluation includes quantitative measures and qualitative data collected through in-depth interviews with people with dementia and family carers; and the cost evaluation includes analysis of data from the Resource Utilisation in Dementia (RUD). The four stage cycle of realist evaluation is adopted, with iterative rounds of theory formulation, data collection and theory testing throughout. DISCUSSION: This realist evaluation of a complex intervention involves a variety of data and perspectives in order to provide confidence in moving from hypothetical constructs about how IHCPs might work to explanations of potential or observable causal mechanisms. In spite of being a key form of service delivery in most healthcare systems, the ways in which home care works to produce the desired outcomes seems to be poorly understood. While there is much descriptive and comparative work, there is a lack of understanding regarding which patient groups might benefit most from home care, or the influence of different service or cultural contexts on outcomes from home care. As well as addressing the core research objectives, this study aims to make a contribution to the underlying theory of home care in ways that can progress our understanding of how outcomes are produced for home care recipients.