The aim of the present study was to determine the factors controlling leptin secretion and to clarify the role of leptin in eating disorders. The subjects were 152 eating-disordered women with different fat mass, eating behavior, and endocrine abnormalities and 24 age-matched control subjects. The body fat mass, eating behavior score, and plasma leptin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), triiodothyronine (T3), free thyroxine (T4), insulin, and cortisol levels were evaluated for each subject. In patients with eating disorder, logarithmic values for leptin were significantly correlated with the body fat mass (r = .828, P < .001), eating behavior score (r = .777, P < .001), and LH (r = .465, P < .001), FSH (r = .440, P < .001), T3 (r = .572, P < .001), insulin (r = .410, P < .001), and cortisol (r = -.389, P < .001) levels. After adjusting for fat mass, the partial correlations of log leptin with LH, FSH, insulin, and cortisol were not statistically significant, but log leptin remained correlated with T3 (r = .390, P < .01). Stepwise regression analysis showed that the body fat mass and eating behavior score were significant determinants of leptin levels. These results suggest that eating behavior, as well as the body fat mass, is the control factor for leptin secretion in eating disorders.