BACKGROUND AND AIMS: Obesity associated with diabetes mellitus is a significant worldwide problem associated with considerable health care costs. Whilst surgical intervention is effective, it is invasive, costly and associated with complications. This study aims to evaluate the safety and efficacy of the EndoBarrier®, a duodenal-jejunal sleeve bypass as an alternative treatment of diabetes mellitus in obese patients. MATERIALS AND METHODS: This was a multi-centre, non-randomised trial recruiting obese patients with type 2 diabetes from three sites in the UK. Eligible participants had a BMI of 30-50 kg/m2and HbA1c levels of 7.5-10%. The study comprised a 12-month period with the EndoBarrier® inserted and a 6-month follow-up period after it had been explanted. The primary study outcomes were weight, BMI, HbA1c levels and fasting insulin and glucose levels. RESULTS: Forty-five patients were recruited and 31 patients (69%) completed the 12-month study period. Significant reductions in weight (95%CI 0.62-29.38; p < 0.05) and BMI (95%CI 1.1-8.7; p < 0.005) were documented 12 months after device insertion. The mean HbA1c was significantly reduced (95%CI 0.1-1.6; p < 0.05) after the device insertion period and reductions in metabolic parameters (fasting insulin and glucose levels) were also documented during the study. Adverse events were also assessed in all patients, the vast majority of which were reported as mild. CONCLUSIONS: The EndoBarrier® appears to be a safe and effective treatment strategy in overweight patients with poor glycaemic control despite medical therapy, or in those who are eligible but decline bariatric surgery.