BACKGROUND Sitagliptin is one of the dipeptidyl peptidase-4 (DPP-4) inhibitors which prevent the inactivation of incretins, increasing the endogenous active incretin levels. Incretins stimulate insulin secretion from pancreatic β-cells and inhibit glucagon secretion from pancreatic α-cells, which is favorable for the treatment of diabetes. Sitagliptin is released on December, 2009, in Japan. We retrospectively studied effects of 6-month-treatment with sitagliptin on glucose and lipid metabolism, blood pressure, body weight and renal function in patients with type 2 diabetes by a chart-based analysis. METHODS We retrospectively studied 220 type 2 diabetic patients who have taken sitagliptin for 6 months by a chart-based analysis. Subjects studied include patients treated with sitagliptin monotherapy, sitagliptin add-on therapy, and switching from glinide to sitagliptin. We selected patients who have both data before and after 6-month sitagliptin treatment and compared the data before the sitagliptin treatment with the data at 6 month after the sitagliptin treatment started. Body weight, blood pressure, plasma glucose, hemoglobin A1c (HbA1c), serum lipids, and estimated glomerular filtration rate in type 2 diabetic patients were measured almost at the same time points before and after 6-month-treatment with sitagliptin. RESULTS Body weight was significantly reduced after 6-month sitagliptin treatment by 0.8 kg. HbA1c levels were also significantly decreased after the sitagliptin treatment by 0.6%. We found a significant and negative correlation between change in body weight and body mass index at baseline. We also observed a significant and negative correlation between change in HbA1c and HbA1c levels at baseline. The number of patients who showed the absence of urinary glucose was significantly increased after the sitagliptin treatment.