Additional Study Information: This is a research study for subjects who have had gastric bypass surgery at least one year ago, and currently have type 2 diabetes. This study is looking at the treatment of diabetes after gastric bypass surgery. About 40% of patients do not experience diabetes remission after gastric bypass surgery. Of the patients who initially go into remission, about 1/3 eventually experience some degree of diabetes relapse in the years following the surgery. The goal of this study is to analyze the effect of sitagliptin (Januvia), a safe and FDA approved medication for the treatment of type 2 diabetes, on glucose levels in patients after gastric bypass surgery. In this study, we will examine whether sitagliptin is an effective and well tolerated medication for patients who have had gastric bypass surgery but have persistent type 2 diabetes. You will get about $xxx for compensation of your time at the end of the study.