Abstract A number of theories have been proposed to explain the substantial comorbidity between the eating disorders and the substance-related disorders. Among them is the claim that self-starvation—exacerbated by excessive exercising—is itself an addiction to the body’s endogenous opioids. While efforts have also been made to identify an “addictive personality,” attempts to establish whether eating-disordered patients share these characteristics have met with mixed success. The present study was designed to determine the degree to which anorexic and bulimic patients display addictive personality characteristics, and whether these traits are useful in predicting the severity of the patients’ weight preoccupation and their degree of excessive exercising. Results confirmed that both anorexic and bulimic patients had high scores on the Addiction Scale of the Eysenck Personality Questionnaire, and that addictiveness and obsessive-compulsiveness were related simultaneously to weight preoccupation and excessive exercising in both patient groups. Findings are discussed within the framework of the auto-addiction opioid theory, and they highlight the similarities and differences in the personality structure of the eating-disorder subtypes.