OBJECTIVES: To estimate the incremental costs following bariatric surgery, with regard to antidepressant use. METHODS: Data was collected for body weight, mental health status such as depression, medication use and counselling for one hundred subjects pre and post bariatric surgery from 2006-2007.    Measures of mental health were compared before and after surgery.  Cost estimates for the management of depression were based on data published in 2000. RESULTS: Patients lost a mean value of 52% of their excess body weight.  Following surgery, the proportion of depressed patients decreased by 46%, the proportion of the patients on antidepressants decreased by 30%, and the proportion of those who utilized counselling services decreased by 19%.  When applying cost estimates for managing depression, total incremental savings in depression management were $6,527 (average per patient per year estimate).   CONCLUSIONS: Bariatric surgery is a costly procedure estimated at $22,213 per procedure. Results from a Western New York center based on 100 patients suggest that reduction in depression and the associated medication and counselling use provide incremental savings of $6527 (per year) for the patients who have the procedure. In addition, co-morbidities associated with obese patients such as diabetes, hypertension, sleep apnea, and venous insufficiency offer further incremental savings which is likely to offset the cost of the bariatric surgery, possibly leading to savings.  Long-term outcomes of bariatric surgery and the associated incremental cost were not evaluated in this study.  Future research should consider long-term outcomes and associated costs from the societal, payer and patient perspectives.  Maintaining the weight loss over the long-term is likely to lead to significant cost savings from all perspectives and improved quality of life.