Chronic idiopathic intestinal pseudo-obstruction is one of the disorders that is most refractory to medical and surgical treatment. Even when patients are given nutritional support, including total parenteral nutrition, obstructive symptoms seldom disappear. We report a case of chronic idiopathic intestinal pseudo-obstruction, due to myopathy, in which hyperbaric oxygenation therapy was strikingly effective. The presence of myopathy was histologically confirmed on the surgically resected jejunal specimen. Hyperbaric oxygenation resulted not only in relief of the patient's obstructive symptoms but also in a rapid decrease of abnormally accumulated intestinal gas. At last, he could resume oral intake without any critical adverse effects. These observations strongly suggest that hyperbaric oxygenation can be an effective therapy in the management of chronic idiopathic intestinal pseudo-obstruction. (Am J Gastroenterol 2000;95: 285-288. (C) 2000 by Am. Coll. of Gastroenterology).