Sacral nerve stimulation (SNS) has become a well-established treatment for patients with fecal incontinence since 1995. The mechanism of action of SNS is still not fully understood but recent studies have shown that the motility of the whole colon is modulated during the stimulation. This modulation of the colonic motility could be a potential mechanism of an action to relieve the symptoms in patients with IBS.

Twenty eight patients with IBS will be enrolled in the study. They have to meet the ROME III criteria, and also satisfy the criteria for implantation of a neurostimulator.

After a post implantation period where the programming of the neurostimulator is optimised, the patient is randomized in a double blinded design to receive either ON-OFF or OFF-ON stimulation in a 2-month period.

At the end of each period (ON/OFF) the patient will be examined with Magnet Tracking System (MTS) for motility and with impedance planimetry including thermal stimulation (circulating water)for multimodal sensory testing of the rectum.

This is based on the study hypothesis that the motility of the small intestine and the colon is changed in IBS patients according to their subtype (Diarrhoea-IBS, Constipation-IBS and Disordered bowel habit-IBS) compared to healthy persons. And that SNS will affect the motility of the small intestine and the colon in IBS patients as well as SNS will affect the perception of pain/discomfort in the rectum in IBS patients.

The effect of ON-OFF-sacral nerve stimulation on the IBS patients and thereby their IBS symptoms will also be evaluated by an IBS score (GSRS-IBS)and on quality of life by an IBS Impact Scale (IBS-IS) as well as the significance of placebo effect in the treatment of patients with IBS with SNS will be evaluated.

Inclusion Criteria:

• Patients aged over 18
• Patients who are psychologically stable and suitable for intervention and able to provide informed consent.
• Patients who are diagnosed with IBS according to the Rome III criteria
• Minimum 30% reduction of the IBS symptoms during the PNE-test (a criteria for implantation of the neurostimulator)

Exclusion Criteria:

• Overt bowel diseases including inflammatory bowel disease
• Pregnant or breast feeding
• Patients who are considered unable to follow the planned programme of the study, including mentally illness or physiological instability
• Patients who are on medication with known influence on gastrointestinal motility including those for thyroid disease, diabetes mellitus, celiac disease and neurological disease