The purpose of this chapter is twofold: on one hand to describe the interviews and questionnaires used to measure personality disorders and on the other hand to reexamine current knowledge of comorbidity between personality disorders and eating disorders. The results of multiple studies do not correspond. There are various reasons for the discrepancies observed: the type of samples used (outpatients or hospitalized patients), sex and age of the patients, the degree of evolution of the disorder (in an acute period, in a situation of chronic phase, or in remission), the differences between the diagnostic criteria used, and the differences between the diagnostic tools used (questionnaires or interviews). The highest rates of personality disorders in patients with eating disorders are obtained with self-questionnaires. The correspondence between self-questionnaires and structured interviews in diagnosing personality disorders in patients with eating disorders is very low. Specifically, the MCMI-II tends to overdiagnose specific personality disorders and, as a result, it is not a good assessment measure for carrying out personality disorder diagnosis. Beyond the above, personality disorders imply a poor prognosis in anorexia and bulimia nervosa. Cluster C personality disorders, particularly obsessive, avoidant, and dependent personality disorders, are the most relevant in anorexia. However, in bulimia, an impulsive temperament and borderline personality seem to be the most significant psychopathological features.