The purpose of this article is to summarize briefly potential biological pathways that are common among anorexia nervosa, bulimia nervosa, and obesity. We conclude that data on serotonergic and beta-endorphin regulatory systems provide the most promising leads for potential trait-based etiological theories. We then discuss the contribution of current data to a better understanding of the etiology and maintenance of eating disorders. Finally, we comment on how the exploration for common biological mechanisms highlights problems in nosological diagnosis (i.e., the lack of symptom specificity among disorders) and obscures the etiological significance of social stressors and cultural factors.