In contrast with theories that try to explain eating disorders mainly resorting to the fear getting fat or to their obsessive components, more and more authors agree that the complexity of this disorder requires specific models in order to fully understand it. These authors indicate the feeling of lack of control as a key element in the origin and maintenance of eating disorders. Using a detailed case study of a purging type of anorexia nervosa, we intend to provide support for this latter approach to the study of eating disorders. The adequate identification of the basic dysfunctional assumptions that comprise the central core of the disorder, as well as the identification of the role of food and weight control when recovering the feeling of [lack of] control and the patient’s identity are presented in this case study. We underscore the importance of both factors in the assessment and intervention in cases with these characteristics.