Studies focusing on the prevalence of obesity in Major Depressive Disorder (MDD), or the impact of excess body fat on the treatment of MDD are lacking. The aim of the present work is to systematically study obesity in MDD outpatients. A total of 369 MDD outpatients enrolled in an 8-wk trial of 20 mg fluoxetine had height and weight measured at baseline. We then examined: (1) the prevalence of being overweight or obese, (2) the relationship between obesity and a number of demographic and clinical variables, and, (3) the relationship between relative body weight and obesity with clinical response. We found that more than 50% of patients were overweight [body mass index (BMI) > or =2 5 kg/m2], while 20% were obese (BMI > or = 30 kg/m2). Obese patients presented with worse somatic well-being scores than non-obese MDD patients, but they did not differ with respect to depression severity, anxiety, somatic complaints, hopelessness or hostility. Greater relative body weight, but not obesity, predicted non-response. In conclusion, greater relative body weight was found to place MDD outpatients at risk for fluoxetine resistance.