Abstract: A prosthesis in the form of a flexible tube having a substantially uniform cross section is disclosed. The prosthesis comprises a flange (2) for endoscopically placing stitches or clips in a hiatal hernia (3), and a flexible tubular portion (1) enabling the tube to be squeezed by exerting a pressure (F) on the outer surface thereof in order to prevent reflux of the stomach contents into the esophagus. Food can pass freely through the prosthesis in the direction from the esophagus (4) to the stomach (5). The prosthesis is made of a biocompatible polymer optionally containing barium sulphate to make it detectable using X-rays.