Despite the existence of codes of ethics, mental health professionals often find it difficult to make decisions about treating patients because their duties to patients may be conflicted. One such case is involuntary treatment for anorexia nervosa, that is, involuntary feeding of the patient without his consent. At this point the question arises to what duty the mental health professional should give priority to: the duty to respect the patient’s autonomy and the right to decide for his treatment himself or the duty to respect the benefit of the patient’s health, even if treatment decision is against his will? In order to make a therapeutic decision, it is important to take into account that a basic feature of anorexia nervosa is the patient’s distorted image of his body that can affect his ability to decide for his health. This fact leads to the question whether there is actually the concept of patient’s autonomy in anorexia nervosa and therefore the therapist’s duty to respect it or whether it is a pseudo-dilemma because the patient’s judgment is not guided by free will, but by his distorted image of his body? Despite in contemporary clinical practice respect for the patient’s autonomy is considered the highest duty of therapist, this research study concludes that moral principles cannot be considered absolute but interpretation and functional hierarchy be required depending of the specifics of each case.