13% of the world's population suffers from obesity and 39% from being overweight, which correlates with an increase in numerous secondary metabolic complications including type 2 diabetes mellitus. Bariatric surgery is the most effective treatment for severe obesity and results in significant weight loss and the amelioration of obesity-related comorbidities through changes in enteroendocrine activity, caloric intake, and alterations in gut microbiota composition. The circadian system has recently been found to be a critical regulatory component in the control of metabolism and thus may potentially play an important role in inappropriate weight gain. Indeed, some behaviors and lifestyle factors associated with an increased risk of obesity are also risk factors for misalignment in the circadian clock system and for the metabolic syndrome. It is thus possible that alterations in peripheral circadian clocks in metabolically relevant tissues are a contributor to the current obesity epidemic. As such, it is plausible that post-surgical alterations in central circadian alignment as well as peripheral gene expression in metabolic tissues may represent another mechanism for the beneficial effects of bariatric surgery. Bariatric surgery may represent an opportunity to identify changes in the circadian expression of clock genes that have been altered by environmental factors, allowing for a better understanding of the mechanism of action of surgery. These studies could also reveal an overlooked target for behavioral intervention to improve metabolic outcomes following bariatric surgery.