Several lines of evidence indicate a role of the brain-derived neurotrophic factor (BDNF) in the modulation of eating behaviour. Therefore, alterations in the physiology of this neurotrophin may be involved in the pathogenesis of eating disorders. In the present study, we investigated serum levels of BDNF in patients with anorexia nervosa (AN), bulimia nervosa (BN) and binge-eating disorder (BED). Ninety-nine drug-free women (27 with AN, 24 with BN, 24 with BED and 24 healthy controls) underwent both a blood sample collection in the morning and diagnostic and psychopathological assessments by means of structured clinical interviews and ad-hoc rating scales. Serum levels of BDNF, 17 beta-oestradiol, FT3 and FT4 were measured. Compared to healthy controls, serum levels of BDNF were significantly reduced in underweight AN women and in normal weight BN women, but not in overweight BED women. Changes in circulating BDNF levels were not affected by the presence of co-morbid depressive disorders. No significant correlation emerged between neurotrophin concentrations and psychopathological, nutritional, demographic and hormonal variables. These findings evidentiate alterations in serum BDNF levels in malnourished patients with AN or BN, but not in well-nourished individuals with BED. Since BDNF seems to exert a satiety effect, its reduction may represent an adaptive change to counteract the decreased calorie ingestion of AN and BN individuals.