In the context of organizational transitions in health care institutions, the decisions taken by leaders and clinicians are informed by multiple sources and by a multitude of actors at all levels of the organization. A study was conducted in the context of a major organizational transition at the McGill University Health Centre in Montreal, Quebec, Canada. The purpose was to examine the body of literature around the notions of “evidence” in decision-making processes in health care. Key informants who had a strategic decision-making role linked to the transition activities were interviewed to explore their perceptions of the types of evidence used to support changes in the organization. Results revealed that managers and clinicians relied on multiple sources of evidence and shared similar concerns about reliability and validity of scant evidence.