The great sociological sucess of the U.S. medical proffesion became established at the beginning of the 20th century. A series of new traits in the doctor patient relationship also became implanted at the same time and have persisted up to the present. This article aims to contribute to a better understanding of this process by analizing some of the circumstances in which it took place. Printed sources, both professional and otherwise, representantive of the period, have been reviewed to archieve this aim. They are analized as follows: the upsurge of medical associationism, the frustation of the plans for a national social security system, medical pretensions with reference to political participation, new professionalist ideals and the increase in legal complaints lodged against doctors. This article also examines some of the significant changes in public declarations of medical ethics. It concludes by affirming that in the USA at the beginning of conceptualization of the profession and the doctor patient relationship which have remained part of current medical practice. Some of these characteristics are: technical profesionalism, voluntarism, contractualism and the trend towards autonomism in the doctor patient relationship.