A procedure for reducing the effective volume of the stomach of a patient involves a balloon module which is introduced into the stomach by either a gastroscope or through a catheter inserted through the stomach wall. The balloon module has a pair of positioning strings and a balloon with an integral protruding tube. After introduction into the stomach, the balloon is inflated and secured in position by the positioning strings. The position of the balloon in the stomach may be monitored by a contrast medium introduced into the balloon.
