Despite the seriously undernourished state of patients with anorexia nervosa and bulimia nervosa, controversial findings have been published regarding some aspects of the immune system that are otherwise impaired in more typical types of malnutrition, such as protein-energy malnutrition. However, cell-mediated immunity is usually altered and the study of immunocompetence has provided useful markers to assess the nutritional status of these patients. In addition, a relative protection against infection has been observed in these patients. Changes in the interactions between the endocrine, central nervous and immune systems are considered relevant to understanding the adaptive mechanisms triggered in these syndromes. The role of cytokines and several hormones are reviewed for their implication in immune homeostasis.