Résumé : Background: An increasing number of surgeons worldwide are now performing one anastomosis/mini gastric bypass (OAGB/MGB). Lack of a published consensus amongst experts may be hindering progress and affecting outcomes. This paper reports results from the first modified Delphi consensus building exercise on this procedure. Methods: A committee of 16 recognised opinion-makers in bariatric surgery with special interest in OAGB/MGB was constituted. The committee invited 101 OAGB/MGB experts from 39 countries to vote on 55 statements in areas of controversy or variation associated with this procedure. An agreement amongst ≥ 70.0% of the experts was considered to indicate a consensus. Results: A consensus was achieved for 48 of the 55 proposed statements after two rounds of voting. There was no consensus for seven statements. Remarkably, 100.0% of the experts felt that OAGB/MGB was an “acceptable mainstream surgical option” and 96.0% felt that it could no longer be regarded as a new or experimental procedure. Approximately 96.0 and 91.0% of the experts felt that OAGB/MGB did not increase the risk of gastric and oesophageal cancers, respectively. Approximately 94.0% of the experts felt that the construction of the gastric pouch should start in the horizontal portion of the lesser curvature. There was a consensus of 82, 84, and 85% for routinely supplementing iron, vitamin B12, and vitamin D, respectively. Conclusion: OAGB/MGB experts achieved consensus on a number of aspects concerning this procedure but several areas of disagreements persist emphasising the need for more studies in the future.