Eating disorders (ED) require more effective psychological interventions, in light of evidence saying that treatment response is often incomplete, and dropout rates are significant. One possible avenue to improve treatment effectiveness is address the frequent comorbidity with personality disorders (PD). When persons suffer from both ED and PD they would present with complex manifestations and serious interpersonal problems. In parallel, their capacity to form a solid working alliance can be limited. They are likely to have difficulty trusting clinicians and engaging in the necessary work needed to counteract their maladaptive ideas about food, weight and body image, and to change their problematic eating habits. This introduction of the issue of the Journal of Clinical Psychology: In Session devoted to treating patients with comorbid ED and PD describe the rationale for why it is necessary to assess and treat PD symptoms integrated with appropriate ED focused treatment.