DPP-4 inhibitors have been used to treat patients with type 2 diabetes mellitus. These agents not only provide glycemic control, but also have other favorable effects, including the prevention of atherosclerosis. However, it has not been determined whether these agents can improve or maintain endothelial cell function. We previously reported the results of two prospective studies assessing the effects of incretin agents on flow-mediated dilation in patients with type 2 diabetes mellitus without severe atherosclerotic diseases. These studies showed that both the DPP-4 inhibitor sitagliptin and the GLP-1 analogue liraglutide did not improve endothelial cell function. This report discusses the effects of sitagliptin on early-stage atherosclerosis and beta-cell function.