In civil and criminal proceedings, there are factors inherent in the role of a treating physician such as advocacy and other duties owed the patient, in contrast to expert opinion provided by an independent assessor which is required to be objective. Misunderstanding or unawareness of the differences in treating versus expert physicians can lead to decision-makers relying on potentially biased information. Recent decisions in Canada have allowed for opinion evidence by treatment providers (Westerhoff v. Gee Estate), which seem to ignore the potential bias of the treatment provider. The lack of clarity by which decision-makers perceive the role of physician witnesses poses a significant issue for physicians, who must balance competing interests, equivocal processes and concerns regarding bias and conflict of interest when providing medical information to a decision-maker. This paper attempts to clarify the essential differences between information provided by a treating physician as opposed to an expert opinion provided by an independent consultant in Canada. Discussion around privacy legislation will be used to highlight some differences. It is hoped that a clearer understanding of the information the decision-makers are receiving will promote an improved understanding of that information and, subsequently, an improved decision-making process.