Knowledge of comorbidity and outcome in anorexia nervosa and bulimia nervosa not only helps us to unravel the largely unknown pathogenesis and nature of these disorders, but it also has practical clinical applications for treatment. Comorbidity studies, for example, by looking at the chronologic order of occurrence of the eating disorders and the most common comorbid psychiatric disorders, help to identify possible causative relationships between them. In addition, these studies identify the disorders that are likely to precede, co-occur with, and complicate treatment of anorexia nervosa and bulimia nervosa. Data from long-term follow-up studies help to characterize the course of these psychiatric diseases, inform patients and clinicians about eating disorders, identify possible treatment-relevant predictors of good and poor outcome, and assist in the planning and design of treatment studies in determining the allocation of appropriate public health resources.

Unfortunately, both studies of outcome and comorbidity are plagued by numerous methodologic difficulties. These include the establishment of consistent and meaningful outcome criteria, the method and areas of functioning assessment, the follow-up method, and a high attrition rate. Recently, more standardized methods of diagnosis and assessment have made data more consistent and interpretable. Results of recent studies on outcome and comorbidity of anorexia nervosa and bulimia nervosa are reviewed here, along with their implications in the continuing quest for a better understanding of and treatment for these often pervasive disorders.