A medical system for the treatment of morbid obesity comprising an inflatable balloon implanted in a gastric cavity, a percutaneous fillant delivery tube and a control module connected to the tube for regulating the inflation and deflation of the balloon. The balloon may be individually contoured and inflated to occupy a large volume of the gastric cavity to provide a feeling of satiety. The balloon may also be deflated to give the gastric cavity lining a rest during less critical time.