On the basis of detailed interviews of females aged between fifteen and twenty-six years with a diagnosis of anorexia nervosa we argue that the autonomy of people with this condition may be severely compromised in four ways, particularly in relation to eating and weight. First there are problems with agency. Second, affective components, particularly anxiety, can dominate beliefs such that the grounds for making a decision may differ from the reasons given in justification. Third, the interactions between the affective components and the objective evidence lead to substantial inner conflicts with resulting lack of stability in preferences and beliefs. Fourth, this lack of stability leads to concerns around identity and authenticity. We argue that some of the ways in which autonomy is compromised reduce competence to decide on treatment. We suggest that these results may be relevant to other mental disorders and have clinical and policy implications.