The cost of health care services and supports for mental health and addictions is important to know. In order to calculate it, one must know "who" is receiving "what" is being provided by "whom" at what "price". Without tracking these types of data, it is difficult to know the cost of the activities being provided. The systematic collection and analysis of such data allows decision makers to become more aware of how money is being spent. Without this information, it is difficult to evaluate different models of care or determine relative responsibilities of different government players. As a case study, we describe the analysis and findings of a project to assess the costs of mental health and addiction services within homeless shelters in Toronto, Ontario, Canada.