OBJECTIVE: Investigate the safety and efficacy of 6 months' duodenal-jejunal bypass liner (DJBL) treatment in comparison with dietary intervention for obesity and type 2 diabetes mellitus (T2DM). BACKGROUND: The DJBL is a bariatric procedure involving an impermeable sleeve that is delivered endoscopically in the proximal intestine. This procedure not only is less invasive than conventional surgical techniques but also has beneficial effects on obesity and T2DM. METHODS: A multicenter randomized controlled trial was conducted. Seventy-seven patients with obesity and T2DM were included. Thirty-eight patients were randomized to 6 months' DJBL treatment in combination with dietary intervention (34 successfully implanted, 31 completed the study), 39 patients received only dietary intervention (controls, 35 completed the study). Total study duration for both groups was 12 months, including 6 months of post-DJBL removal follow-up. RESULTS: After 6 months, just before DJBL removal, the DJBL group had lost 32.0% [22.0%-46.7%] of their excess weight versus 16.4% [4.1%-34.6%] in the control group (P < 0.05). Glycated hemoglobin A1c levels improved to 7.0% [6.4%-7.5%] in the DJBL group and to 7.9% [6.6%-8.3%] in the control group (P < 0.05). In addition, 85.3% of DJBL patients showed decreased postprandial glucose excursions versus 48.7% of control patients (P < 0.05). At 12 months, excess weight loss of the DJBL group was 19.8% [10.6%-45.0%] versus 11.7% [1.4%-25.4%] in the control group (P < 0.05). HbA1c was 7.3% [6.6%-8.0%] versus 8.0% [6.8%-8.8%], DJBL versus control respectively (P = ns). CONCLUSIONS: The DJBL is a safe and effective alternative to invasive bariatric procedures. Six months of DJBL treatment combined with diet leads to superior weight loss and improvement of T2DM when compared with diet alone.