Objective: This study investigated the role of leptin on eating behavior and reproductive function in eating disorders. Method: The subjects included 80 eating-disordered women, having different fat mass, eating behavior, and endocrine abnormalities, and 26 control women. Plasma leptin, insulin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), cortisol, insulin growth factor-1 (IGF-1), free T(4) levels, percent body fat, eating behavior score, and menstrual status score were evaluated for each subject. Results: In eating-disordered patients, log of leptin levels were significantly correlated with body fat mass, eating behavior score, menstrual status score, and insulin, LH, and FSH levels. Stepwise regression analysis showed that fat mass and eating behavior score were significant determinants of leptin levels. Furthermore, in patients undergoing recovery, leptin levels were determined by fat mass and/or eating behavior. Discussion: These results suggest that leptin may play some role in counteracting the abnormal eating behavior, reproductive function, and fat mass in these disorders.