Described herein are endoscopic staplers used to apply one or more fasteners to body tissue. In one embodiment, a fastener-applying device, which is preferably a stapler, is passed transorally into the stomach and used to plicate stomach tissue by engaging tissue from inside of the stomach and drawing it inwardly. In the disclosed embodiments, the tissue is drawn inwardly into a vacuum chamber, causing sections of serosal tissue on the exterior of the stomach to be positioned facing one another. The disclosed staplers allow the opposed sections of tissue to be moved into contact with one another, and preferably deliver staples for maintaining contact between the tissue sections at least until serosal bonds form between them. Each of these steps may be performed wholly from the inside of the stomach and thus can eliminate the need for any surgical or laparoscopic intervention. After one or more plications are formed, medical devices may optionally be coupled to the plication(s) for retention within the stomach.