A systematic review of dementia cost-of-illness (COI) studies in the US and Canada was conducted to explore the policy-making relevance of these studies. MEDLINE, CINAHL, EconLit, AMED and the Cochrane Library were searched from inception to March 2010 for English-language COI articles. Content analysis was used to extract common themes about dementia cost from the conclusions of articles that passed title, abstract and full-text screening. These themes informed our exploration of the policy-making relevance of COI studies in dementia. The literature search retrieved 961 articles and data were extracted from 46 articles. All except three articles reported data from the US; 27 articles included Alzheimer's dementia only. Common themes pertained to general observations about dementia cost, cost drivers in dementia, caregiver cost, items that may lower dementia cost, social service cost, Medicare and Medicaid cost, and cost comparisons with other diseases. The common themes suggest policy-oriented research for the future. However, the extracted COI studies were typically not conducted for policy-making purposes and they did not commonly provide prescriptive policy options. Researchers and policy makers need to consider whether the optimal research focus in dementia should be on programme evaluations instead of more COI studies.