Abstract Background Eating disorders (ED) and substance use disorders (SUD) display clinical and psychodynamic analogies. The co-diagnosis of a substance use disorder in male ED patients is frequent. Nevertheless, knowledge about the mutual predisposing factors or personality analogies is currently scarce and hypotheses are controversial. Methods The Temperament and Character Inventory (TCI) was used to assess 21 anorectic men, 79 heroin-dependent men, and 75 control men matched for age and education. Results Anorectic and opiate-addicted patients displayed higher Harm Avoidance and lower Self-directedness and Cooperativeness. Anorectic men displayed lower Reward Dependence and higher Persistence. Opiate addicts had higher Novelty Seeking and Self-transcendence. Discussion Anorectic and heroine-dependent subjects share personality traits related to anxiety, fearfulness and antisocial features. Nevertheless, the personality profile does not completely overlap and this could influence the choice of the “substance” of abuse and the related clinical differences between anorexia and heroin dependence.