This paper argues for a normative conception of medical professionalism based on the work of sociologist Talcott Parsons. Such a conception grounds medical professionalism on the expert authority of the physician; the concept of authority is therefore discussed at length. Parsons view also lays much stress on the fact that the proper exercise of medical authority nearly always involves aligning the interests of individual patients with those of society at large. Parsonian professionalism looks to professional institutions such as medical schools, societies and journals to secure the competence and ethical behavior of professionals, and to help ensure that professionals exercise of authority is never biased by private financial interests or by public political power. Professional institutions should encourage professionals to develop a set of preferences and desires (e.g., for respect of their peers, and not for power or financial gain) that will tend to make them trustworthy authorities.