[From diagnosis to symptoms].

The diagnosis of anorexia nervosa is one of the easiest to make in that it is a positive diagnosis, not a differential diagnosis. It is defined by a few criteria which together become almost pathognomonic: excessive restriction of energy intake combined with an irrational fear of weight and an altered body image. Even if weight is at the heart of the medical team's concerns, it is important to question the pathology in its history, in order to put it in to context, and sometimes to understand the para-logic and its function in the patient's life history. It is necessary to work on emotions and cognitions in addition to behaviour.