Type 2 diabetes mellitus is a common chronic disease that causes significant morbidity and mortality worldwide. The primary goal of treatment is to target glycemic control by maintaining the glycosylated hemoglobin level near 6-7% without predisposing patients to hypoglycemia. Diabetes results from a combination of increased hepatic glucose production, decreased insulin secretion from beta cells, and insulin resistance in the peripheral tissues. Currently available antidiabetic agents work by different mechanisms to lower blood glucose levels. Unfortunately, each of them has its tolerability and safety concerns that limit its use and dose titration. Sitagliptin is the first antidiabetic agent from the class of dipeptidyl peptidase-4 enzyme inhibitors. It increases the amount of circulating incretins, which stimulate insulin secretion and inhibit glucose production. Sitagliptin was approved by the US Food and Drug Administration (FDA) for use with diet and exercise to improve glycemic control in adult patients with type 2 diabetes. It can be used alone or in combination with metformin or a thiazolidinedione (pioglitazone or rosiglitazone) when treatment with either drug alone provides inadequate glucose control. The usual adult dose is 100 mg once daily. A dose of 25-50 mg once daily is recommended for patients with moderate-to-severe renal impairment. In randomized, placebo-controlled trials that lasted for up to 6 months, sitagliptin lowered glycosylated hemoglobin levels by 0.5-0.8%. In a 52-week clinical trial, sitagliptin was shown to be noninferior to glipizide as an add-on agent in patients inadequately controlled on metformin alone. Sitagliptin was well tolerated with the most common side effects being gastrointestinal complaints (up to 16%), including abdominal pain, nausea and diarrhea; hypoglycemia and body weight gain occurred at similar rates compared with placebo. Overall, sitagliptin provides a treatment option for patients with type 2 diabetes as a monotherapy, or as an adjunct to metformin or a thiazolidinedione when patients achieve inadequate glycemic control while on either of the agents. It is also an alternative therapy for those patients who have contraindications or intolerability to other antidiabetic agents.