The present GUARD study was a prospective, non-interventional study evaluating the clinical effectiveness, safety and tolerability of vildagliptin with or without metformin in adult patients with type 2 diabetes mellitus (T2DM) studied in routine clinical practice. Patients were enrolled from countries across four geographical regions. The primary endpoint was change in glycated haemoglobin (HbA1c) concentration from baseline after 24 weeks of treatment with vildagliptin with or without metformin. Of 19 331 patients analysed, 3511 received vildagliptin and 15 820 received vildagliptin plus metformin. At week 24, the mean HbA1c was reduced significantly from baseline by -1.27% (vildagliptin: -1.17%; vildagliptin plus metformin: -1.29%; p < 0.0001). Significant reductions in HbA1c from baseline were consistently reported regardless of patient age, body mass index (BMI) or baseline HbA1c. Weight and BMI were also significantly reduced from baseline. Vildagliptin treatment with or without metformin was generally well tolerated. It provided clinically relevant glycaemic and weight control, and was well tolerated in a large multi-ethnic population of patients with T2DM studied in routine clinical practice