Hypnosis is a state of highly focused attention (trance) in which external stimuli are disattended and suggestion becomes far more effective than usual.1 The fundamental usefulness of hypnosis in medicine and healing has been controversial for more than 200 years, ie, since Anton Mesmer produced the body of work now recognized as the beginning of clinical hypnosis. Does medical hypnosis work? If so, how? Does it produce real bodily healing at the physiologic level, or is its therapeutic effect merely the result of imagined comfort—and thus to be found in the mind only? These questions are reasonable and can best be addressed by clinical observation aided by modern technology.