Vildagliptin is a dipeptidyl peptidase-4 (DPP-4) inhibitor that is being evaluated in the treatment of patients with type 2 diabetes mellitus. It improves glycaemic control by inhibiting DPP-4 from inactivating the incretin hormones glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide, prolonging incretin activity in response to ingestion of nutrients. This allows for increased insulin sensitivity, decreased glucagon secretion and improved beta-cell function in a glucose-dependent manner. Glycaemic control with vildagliptin 50 or 100 mg/day, measured by a change from baseline in mean glycosylated haemoglobin (HbA(1c)) at study endpoint, was improved relative to placebo in several well designed clinical trials of vildagliptin monotherapy in patients with type 2 diabetes. In randomised active comparator studies, noninferiority of vildagliptin in reducing HbA(1c) levels from baseline was established to rosiglitazone, but not to metformin. Vildagliptin also showed efficacy in reducing HbA(1c) levels in patients with type 2 diabetes when used in combination with metformin, pioglitazone or insulin. Vildagliptin was generally well tolerated when administered alone or in combination with additional antidiabetic treatment. Gastrointestinal adverse events were mild to moderate in intensity, and occurred less frequently than with metformin. Hypoglycaemic events were rare and occurred at a similar incidence to that with placebo.