OBJECTIVES: The IBIS-C study, currently ongoing, is the first to assess the burden of IBS-C in 6 European countries (France, Germany, Italy, Spain, Sweden, UK) . We present an interim analysis of the retrospective data from Spain. METHODS: This is an observational, retrospective-prospective (±6-months(m)) study in patients diagnosed in the last five years of IBS-C (Rome-III criteria) of moderate-to-severe degree (IBS-Symptom Severity Score(IBS-SSS)≥175). Quality-of-life(QoL) was assessed with the EuroQoL-5D(EQ-5D) and IBS-QoL. RESULTS: We included 46 patients (62% severe, mean(±SD) 44.6±12.2 years, 83% women, time since diagnosis 2.8±3.6 years). According to IBS-SSS, 94% had abdominal pain in the last month (62% of time) and 85% abdominal distention. Other prevalent symptoms were: constipation (96%), abdominal discomfort (72%) and bloating (59%). Mean IBS-QoL was 46±23, on a scale 0-100 (worst QoL), and the most affected domains were "food avoidance" (mean:64) and "health worry" (60). Mean EQ-5D was 51±20, on a scale 0-100 (best QoL), and 93% and 70% of patients, respectively, reported problems in pain/discomfort and anxiety/depression. In the previous 6m, 83% of patients consulted a primary care physician, and 89% a specialist (mostly a gastroenterologist)(mean(95%CI):2.8(1.4-4.3) and 2.0(0.9-3.1) visits, respectively). 20% of patients required emergency department visits or hospitalization (mean stay:1.3(0.6-1.9) days). 76% of patients underwent a diagnostic test (mean:2.1(1.3-2.9) tests). 89% of patients took medication (63% prescription drugs and 54% OTC medications), 26% received complementary therapies. The mean direct costs per patient for the National Health System(NHS) were €1,025/6m(549-1627) and the mean costs for the patient were €200/6m. 17% of patients had sick leave(mean:3.5 leaves; mean duration:58 days) and 46% had productivity losses(mean:49 hours). Mean indirect costs were €991/6m. Total costs amounted to €2216/6m. CONCLUSIONS: Moderate-to-severe IBS-C has a great impact on healthcare resource utilization and productivity of patients, and the results suggest significant costs to the NHS and society. QoL can be severely affected.