Rationale: Sitagliptin has been extensively studied in patients with type 2 diabetes mellitus, but there are no documented studies in the literature to establish a safe and efficacious dose in type 1 diabetes mellitus. Our previous experience with exenatide, which is a GLP-1 agonist and also with similar end pharmacological effects as Sitagliptin and other related published studies suggest that to avoid immediate post-prandial hypoglycemia insulin dose needs to be reduced when patients administer glucagon suppressors in conjunction with insulin. Hence, the dose of insulin will be decreased by 20-50% when Sitagliptin will be administered.