This is a multicentre, nationwide and cross-sectional study carried out in China, covering 30 sites and 3000 patients totally. As for the ratio of tertiary to secondary general hospitals is approximately 1:4 in China, 6 tertiary and 24 secondary hospitals will be randomly selected in this study.To adapt the representativeness of the data with the operational feasibility, 30 tertiary and 120 secondary hospitals will be randomly selected over the 6 geographic regions (north, northeast, east, south central, southwest and northwest). Among those, 1 tertiary and 4 secondary hospitals in each region will be further selected based on GI department setup, willingness to participate in the study, capability and primary investigator's consideration. Within participated hospitals, subjects will be enrolled consecutively from all the outpatients of GI department to minimize selection bias. 3000 subjects will be allocated to tertiary and secondary hospitals with a ratio of 1:1. In general, 250 subjects will be enrolled from tertiary hospitals and 250 subjects will be enrolled from secondary hospitals for each region. During the subject enrolment, the investigator will firstly explain the purpose of the study to consecutive GI patients and written informed consents will be obtained. Then qualified patients will be given a questionnaire and finish it during waiting time. After receiving questionnaires, IBS diagnosis will be made by investigators based on Rome III or Rome IV IBS diagnostic criteria. Subjects will be identified as medically diagnosed with IBS if they have been diagnosed by their clinicians. And subjects will be classified as IBS sufferers without medical diagnosis if they satisfy Rome III or Rome IV diagnostic criteria and have not received IBS diagnosis from physicians. For IBS patients, either medically diagnosed or diagnosed with IBS criteria, investigators will collect all the information on demographic features, disease characteristics and current treatment status. For non-IBS patients, only demographic information will be collected.