Anorexia nervosa is a very serious and often chronic eating disorder. Egosyntonicity is one of the core features of anorexia nervosa which refers to the sense of the anorexia nervosa experienced by many patients being a part of themselves or of their identity. It seems to be responsible for the denial of illness and resistance to treatment. Many researchers stress the very role of a sense of identity in the course of anorexia nervosa. Unfortunately, it is underestimated especially in the context of discussions about capacity in anorexia nervosa. The concept of capacity currently in use, which is based on understanding and reasoning, does not capture the difficulty that arises from the impact of anorexia nervosa on the sense of personal identity. Therefore, the egosyntonicity should be considered as a key to a new proposition of capacity assessment in anorexic patients.