Reliable patient reported outcome measures (PROM's) for symptom assessment in irritable bowel syndrome are essential in order to investigate natural disease course and potential treatment options aimed at symptom improvement, since biological markers are currently unavailable. Currently used symptom assessment methods, i.e. end-of-day or end-of-week questionnaires, have considerable limitations. The Experience Sampling Method (ESM), an electronic questioning method characterized by random and repeated, momentary assessments in the subject's current state and environment, might overcome these limitations. Aim of this study is to validate an IBS-specific electronic patient-reported outcome measure, based on the Experience Sampling Method-principle, for symptom assessment in IBS.

Inclusion Criteria:

• Diagnosis of irritable bowel syndrome according to Rome IV criteria.
• Ability to understand and speak the national language of the concerning center.
• Ability to understand how to utilize the ESM-tool.

Exclusion Criteria:

• Any organic explanation for the abdominal complaints.
• A history of abdominal surgery, except for uncomplicated appendectomy, laparoscopic cholecystectomy and hysterectomy.
• Start up of regularly used medication from one month before inclusion until the end of study participation.

IBS patients.