A device for forming a stoma opening in the stomach or esophagus of a patient comprises an elongated restriction member (2), forming means (10) for forming the elongated restriction member into at least a substantially closed loop around the stomach or esophagus, said loop defining a restriction opening (3), and an adjustment means (12) for adjusting the restriction member in said loop to change the size of said restriction opening. The adjustment means (12) is designed to mechanically adjust the restriction member in a non-invasive manner to allow post-operation non-invasive adjustments of the restriction member.Linvention concerne un dispositif pour former une stomie dans lestomac ou loesophage dun patient. Ledit dispositif comprend un élément de restriction allongé (2), un moyen de formage (10) pour former lélément de restriction allongé de sorte quil que se présente sous la forme dau moins une boucle sensiblement fermée, autour de lestomac ou de loesophage, ladite boucle définissant une ouverture de restriction (3), et un moyen dajustement (12) pour ajuster lélément de restriction dans ladite boucle et modifier la taille de ladite ouverture de restriction. Le moyen dajustement (12) est conçu pour ajuster mécaniquement lélément de restriction de manière non invasive, ce qui permet les ajustements non invasifs post-opératoires de lélément de restriction.