OBJECTIVE: Compare the resource use between IBS patients and non-IBS subjects (controls), in order to estimate the burden of IBS. METHODS: Observational, prospective study including a sample of 455 IBS patients, meeting Rome II criteria, and 69 controls. The controls were selected from those subjects who had attended a health centre with a relative due to digestive problems (excluding IBS). Both samples were selected from the consulting rooms of 86 Spanish gastroenterologists and physicians. Patients and controls attended a total of five visits at three-month intervals, making a total follow-up period of one year. During the first month after each visit patients completed a diary including information about resource use. Indirect resources and drugs use were registered in the patients' diary and other direct resources were registered in follow-up medical controls. RESULTS: The results presented are preliminary and corresponding to prospective information obtained from the first 3 months' follow-up. The patients mean (SD) age was 43 (14) years and 76.5% were female. Patients and controls were of the same age and gender. 52.6% of IBS patients and 29% of controls visited a clinic at least ones (p<0.01), 2% of patients were hospitalised and 14.2% of patients visited an emergency ward at least ones. The cost associated with resources used was almost three times higher in patients than in controls (p<0.01). In terms of indirect resources, 35.8% of patients and 20% of controls experienced limited or reduced performance at work during the month following the baseline visit (p<0.05). The mean cost associated with absence from work at one month was also higher for patients (€100.34) than for controls (€37.12) (p<0.01). CONCLUSIONS: IBS is associated with an important burden in terms of direct and indirect costs, IBS patients using more health resources and experiencing a higher productivity loss.