Nineteenth century philosophy and anatomy regarded the nervous system as the only pathway of communication between the brain and body but now, research in the field of psychoneuroimmunology (PNI) has provided evidence to prove the age-old belief that there is a connection between the mind (or mental/emotional states) and the body. Researchers in PNI have now shown that the communication between the nervous and immune systems is bi-directional – i.e. there is a psychological reaction to physical disease and a somatic presentation of psychological disorders - and that the immune system, the autonomic nervous system, the endocrine system and the neuropeptide systems all communicate with each other by means of chemicals called messenger molecules or ligands. This paper outlines research into the treatment of Irritable Bowel Syndrome (IBS) with hypnotherapy, taking into account the mind-body connection and treating both the patient’s physiological and emotional/psychological symptoms rather than treating the physiological symptoms only. In other words, using a more holistic approach to the treatment of IBS. IBS is probably the most common functional gastrointestinal disorder encountered by both gastroenterologists and physicians in primary care. It is estimated that from 10% to 25% of the general population suffer from this condition and that it comprises about 30-50% of the gastroenterologists’ workload, yet the aetiology of IBS is unknown and, so far, there is no cure. Researchers are beginning to view IBS as a multi-faceted disorder in which there appears to be a disturbance in the interaction between the intestines, brain, and autonomic nervous system, resulting in an alteration in the regulation of bowel motility and/or sensory function. Most researchers agree that a subset of IBS sufferers have a visceral hypersensitivity of the gut or, more specifically, an increased perception of sensations in the gut. To date, studies of IBS have proposed previous gastroenteritis, small intestine bacterial overgrowth, psychosocial factors, a genetic contribution, and an imbalance of neurotransmitters as either possible causes or playing a part in the development of IBS. It is generally agreed that a patient’s emotional response to stress can exacerbate the condition. In section 1 of the thesis, the introduction, a detailed description and background appropriate to the study undertaken are provided, including aspects of epidemiology, diagnostic symptom criteria and clinical relevance of the Irritable Bowel Syndrome. Previous studies of various forms of treatment for IBS are discussed with the main emphasis being on treatment with hypnotherapy. All these therapies have concentrated on either mind or body treatments whereas this study demonstrates how hypnotherapy, and the use of imagery, addresses both mind and body. Finally, the rationale for the current study and the specific aims of the thesis are outlined. In section 2, the methodology and assessment instruments used in the clinical trial are discussed, as well as recruitment processes, research plan and timetable, and treatment schedule. Statistical analyses are provided and the main outcomes measures of the clinical trial, its limitations and scientific implications are addressed.