To assess lymphocyte stimulation and lymphocyte phenotype evaluation in adolescent patients with anorexia nervosa (AN). Method: In vitro lymphocyte stimulation and flow cytometric phenotype studies were done on 26 hospitalized patients with AN receiving nutritional rehabilitation. The laboratory assessment consisted of lymphocyte subset analysis and in vitro lymphoproliferative responses to mitogens and antigens. Results: Flow cytometric phenotype analysis showed that only a minority of the patients had abnormal phenotype and immune responses, moreover their immune systems were not significantly impaired. Discussion: The cytofluorometric study of immune function does not show significant alterations in adolescents hospitalized for anorexia nervosa. © 1996 by John Wiley & Sons, Inc.