Hypnotherapy has been investigated for 30 years as a treatment for gastrointestinal (GI) disorders. There are presently 35 studies in the published empirical literature, including 17 randomized controlled trials (RCTs) that have assessed clinical outcomes of such treatment. This body of research is reviewed comprehensively in this article. Twenty-four of the studies have tested hypnotherapy for adult irritable bowel syndrome (IBS) and 5 have focused on IBS or abdominal pain in children. All IBS hypnotherapy studies have reported significant improvement in gastrointestinal symptoms, and 7 out of 10 RCTs in adults and all 3 RCTs in pediatric patient samples found superior outcomes for hypnosis compared to control groups. Collectively this body of research shows unequivocally that for both adults and children with IBS, hypnosis treatment is highly efficacious in reducing bowel symptoms and can offer lasting and substantial symptom relief for a large proportion of patients who do not respond adequately to usual medical treatment approaches. For other GI disorders the evidence is more limited, but preliminary indications of therapeutic potential can be seen in the single randomized controlled trials published to date on hypnotherapy for functional dyspepsia, functional chest pain, and ulcerative colitis. Further controlled hypnotherapy trials in those three disorders should be a high priority. The mechanisms underlying the impact of hypnosis on GI problems are still unclear, but findings from a number of studies suggest that they involve both modulation of gut functioning and changes in the brain's handling of sensory signals from the GI tract.