A gastrointestinal implant device 600 comprises a sleeve 601 for extending into the duodenum and an artificial valve 602 for placement at the pylorus 603 to control flow from the stomach into the duodenal sleeve 601. A support structure for the valve comprises a scaffold 605 to which the valve 602 is mounted and a luminal prosthesis 606. The luminal prosthesis 606 comprises a proximal flare 620 for location at the antrum of the pylorus, a bulbous region 621, and a scaffold receiving region 606.
