Leptin is a product of the obese gene and plays an important role in the regulation of body weight and food intake. Weight and appetite are frequently altered in depression. So far, inconsistent results have been reported in terms of leptin levels in depression. Therefore, the authors investigated serum leptin levels in patients with depression and in healthy controls, and whether there was any alteration throughout antidepressant treatment. Female patients showed significantly higher leptin levels than those of the control females both before and after the response to antidepressant treatment, whereas no difference was found between the male patients and the male controls. The improvement from depression with antidepressant treatment caused a further elevation on the leptin levels, in both female and male patients. These findings confirm an increase in leptin levels in depressive patients and presence of a sexual dimorphism. Moreover, clinical response to antidepressant treatment seems to have an additional increasing effect on leptin levels.