The principle of informed consent, aimed at the lawfulness of health assistance, tends to reflect the concept of autonomy and of decisional autodetermination of the person requiring and requesting medical and/or surgical interventions. This legal formula, over the last few years, has gained not only considerable space but also importance in the doctrinal elaboration and approaches, as well as juridical interpretations, thereby influencing the everyday activities of the medical profession. Informed consent is still the object of continuous explorations, not only asfar as concerns the already confirmed theoretical profile but, instead, the ambiguous practical and consequential aspect. Analysing how the concept and role of consensus was born and developed with the more adequate and reasonable excursions to make it valid and obtain it, it is impossible not to take into consideration, on the one hand, the very ancient philosophical origins and, on the other, the fact that it was conditioned by religion with the moral aspects and the accelerated deontological evolution with pathways parallel to the needs and the progress offered by new forms of treatment and novel biotechnological applications. The principle of consent is a relatively new condition. In fact, already in the times of not only the Egyptian civilisation, but also the Greek and Roman, documents have been found which show how the doctor's intervention had, in some way, first to be approved by the patient. Plato (law IV) had already foreseen the problems, the procedures and the modes of information which are, in synthesis, at the root of the principles of the present formula of informed consent and correlated the practice of the information and consensus with the quality and social position of the patient. The only guarantee that the patient might have, derived from a fundamental principle of medicine of all times: "in disease, focus on two aims, to improve and not to cause damage". A figure can be recognised, in the Hippocratic physician, that cared about the patient's suffering, but never neglected looking after his own outcome, endeavouring to avoid becoming involved in lack of success and death of a patient. The concept of consensus is inexistent, albeit, there is an awareness of the presence of precautious and preventive information. In the behaviour of doctors, in ancient times, it is not difficult to recognize the true motives and the real reasons that, already in those days, give rise to the necessary "defensive medicine" particularly as far as concerns the social status of the patient. Already from the early origins, continuing the Hippocratic tradition, the relationship between doctor and patient was consolidated, based upon two very definite criteria, represented, on the one hand, by the professional duty of the physician to do what is bestfor the patient and, on the other, the duty of the patient to completely accept the physician's decisions and intervention. The Hippocratic physician respected a principle of professional responsibility which was more religious and of a moral type, but, from a legal point of view, very weak inasmuch as it depended upon regulations elaborated by human beings. The conviction and certainty that the physician acted, in the interest of his patient's well-being, has been passed down over the centuries endowing the physician with moral authority and a kind of legal impunity, conditions which corresponded, in an almost reflection-likefashion, with the duty of obedience and subjection, on the part of the patient. Christianity was grafted into this consolidated vision of the sacral character of medicine and medical practice, which did not substantially change the Hippocratic type of ethical behaviour. Non only the population but also the Christian physician was aware of the religious importance of his intense activity as a mission and compared to a special kind of priesthood in safe-guarding health, considered as a gift of God. Therefore, invested with this authority which derived from his professional role and from his very work, he felt it his duty to guide the patient, deciding and for him. The patient is an ignorant person who does not have the knowledge, the intellectual capacity or moral authority to oppose or disagree with the wishes and decisions of the physician who, instead, on account of his doctrine, knows exactly what is goodfor him. In this regard, if we were to speak of consensus concerning the physician's intervention, he would be considered useless in as much as obvious and understood when seeking help. The attitude of the patient towards the physician has always tended to one of strong faith and characterized by psychological subjection borne out by traditions thousands of years old. A patient who was sick, again, as an attitude of respect and gratitude, followed the treatment but never asked for any explanations regarding the therapeutic effects and the physician refrained from taking any initiative to inform the patient or his/her family. Each phenomenon, therefore, has a precise origin, a well-defined history and when its importance tends to significantly condition the activities concerning Man, a desire emerges to learn the origin and the history. As is well known, a trial commenced in Nuremberg, on December 19, 1946, of Nazi doctors and a code was defined in which the judges, all Americans, clearly emphasized a view of medical research and technology: science should never transform or consider human beings as an instrument to be employed for scientific purposes. In actual fact, documents exist providing evidence that a few decades before the drawing up of the Nuremberg Code, the need had been expressed, in Germany itself to somehow make medical interventions and actions legal by means of the use and practice of consensus. The moral and ethical principles in those documents, even if not available as bibliographic references in the English literature, certainly merit, from a historical viewpoint to be considered as conceptual elements and doctrinal and socio-cultural products, even if at that time, of little practical importance, which belong to the European culture and, in particular, and almost paradoxically, in the light of what happened, to the German culture. The United States of America is held to be the country of origin of informed consent, the initial aim of which was make sure that the correct dignity of the patient's independence be reserved at the time of decision making and choice of medical options. Reports on this topic, in fact, first appeared in the USA, at the beginning of the 18th Century, with problems focusing on and limited to only the simple rights of the patient in giving his/her approval of the health intervention later to be conceptually developed, along the lines of an itinerary with, at intervals, famous legal actions, until in the 20th Century, informed consent was reached, a criterion that, as is well known, foresees and includes not only the important and fundamental autonomy of the patient to decide, which stems ones personal rights, but also the essential objective element, which is, information. The expression informed consent has simply been transposed in Italian and roughly translated in an ambiguous fashion into "consenso informato" when, on the contrary, it should be referred to as "informazione per il consenso" "information for consensus" not only to respect the concept but, surely, for a more correct deciphering and a more precise interpretation related to the numerous concepts it presupposes and implies. Information and consent may be compared to the two sides of the same coin. These are the two important pillars that coincide and are joined giving weight to the medical responsibility, as far as concerns consent to the health intervention: on the one hand, having obtained consent,following correct and sincere information interpreted and deciphered as an important phase and an essential indicator of correct, scrupulous medico-professional procedure and, on the other, the consensus itself conceived as a duty aiming at the maximum respect of the rights to autodetermination, independence and autonomy of the patient, as a person. At the beginning of the Nineties, as we have seen, we were made aware of a series of legal actions regarding medical responsibility which was greatly conditioned by the Anglosaxon influence which initially induced many Italian magistrates and forensic physicians to adopt an extremely rigid attitude with no attempt to comply, in any way, with the culture and traditions of our country and our tradition which has always been inspired by good common sense, both medical and human. The American experience has been very rapidly adopted, by some, without a profound, complete and necessary historical and evolutional analysis aimed at those intertwined principles that have been motifs that have gradually led to the legal references in those emblematic cases referred to, the conclusions of which continue to attract a great deal of attention. In Italy, the legal and doctrinal evolution of informed consent, even if following a little more rapidly the traces, steps, problems and interpretations of the various aspects drawn up, characterized and applied in the United States, has not only occurred at a later time, but, despite reaching the same meaningful objectives, the same considerations, the same importance, and, unfortunately, the same inconveniences, has had quite different aims, approaches and articulations. In this respect, it is enough to focus attention on the different cultural traditions and religious routes, on the different doctrinal background, the particular historical origins and the individual legal aspects, all extremely different one from the other. (ABSTRACT TRUNCATED)