The present invention provides methods and apparatus for endoluminally performing gastroplasty. In one variation, the apparatus comprises a sizing tube, and a steerable guide that may be reversibly disposed within the sizing tube. In another variation, the sizing tube and steerable guide are integrated into a single device. In one method of utilizing the apparatus, a pouch is endoluminally formed within a patient's stomach, thereby partitioning or reducing the stomach and restricting the flow of food therethrough. The pouch may form a Vertical Banded Gastroplasty or Magenstrasse and Mill in an endoluminal fashion. Advantageously, the sizing tube or steerable guide may be used to properly size the endoluminal pouch.