Evidence-based healthcare focuses on the need to use interventions that are supported by the best available and most up-to-date evidence or knowledge. Many clinical questions cannot be fully answered by evidence derived from quantitative or qualitative research designs alone, since many areas in healthcare are supported by clinicians' tacit knowledge derived from their clinical experiences. In this situation, evidence generated from a systematic review of text and opinion may be required as the best available evidence. The aim of this study is to highlight the importance and role of expert opinion synthesis in healthcare, and present results of an international methodological group review.