For adult patients with type 2 diabetes mellitus, Sitagliptin SUN is indicated to improve glycaemic control: as monotherapy:- in patients inadequately controlled by diet and exercise alone and for whom metformin is inappropriate due to contraindications or intolerance. as dual oral therapy in combination with:- metformin when diet and exercise plus metformin alone do not provide adequate glycaemic control.- a sulphonylurea when diet and exercise plus maximal tolerated dose of a sulphonylurea alone do not provide adequate glycaemic control and when metformin is inappropriate due to contraindications or intolerance.- a peroxisome proliferator-activated receptor gamma (PPAR?) agonist (i.e. a thiazolidinedione) when use of a PPAR? agonist is appropriate and when diet and exercise plus the PPAR? agonist alone do not provide adequate glycaemic control. as triple oral therapy in combination with:- a sulphonylurea and metformin when diet and exercise plus dual therapy with these medicinal products do not provide adequate glycaemic control.- a PPAR? agonist and metformin when use of a PPAR? agonist is appropriate and when diet and exercise plus dual therapy with these medicinal products do not provide adequate glycaemic control. Sitagliptin SUN is also indicated as add-on to insulin (with or without metformin) when diet and exercise plus stable dose of insulin do not provide adequate glycaemic control.