Methods and apparatus for performing malabsorptive bypass procedures within a patient's gastrointestinal lumen are described comprising, for example, gastroenterostomy procedures that are preferably performed in an endoscopic or laparoscopic fashion. Anastomosis between the patient's stomach and intestine allows food to bypass at least a portion of the patient's stomach and/or intestine, thereby providing a malabsorptive region. The malabsorptive procedure may be accompanied by additional procedures, for example, pyloric occlusion, pyloroplasty, gastroplasty, gastric tissue destruction and/or intestinal pleating.