BACKGROUND: There is a need for safe and effective IBS treatments that provide immediate and sustained improvement of IBS symptoms, particularly among more severe patients. The aim was to assess long-term clinical response of cognitive behavioral therapy (CBT) with reference to IBS education. METHODS: A total of 436 Rome III-diagnosed IBS patients (80% F, M age = 41 years) were randomized to: 4 session home-based CBT (minimal contact (MC-CBT)), 10 session clinic-based CBT (standard (S-CBT)), or 4 session IBS education (EDU). Follow-up occurred at 2 weeks and 3, 6, 9, and 12 months following treatment completion. Treatment response was based a priori on the Clinical Global Improvement Scale (global IBS symptom improvement) and IBS Symptom Severity Scale (IBS-SSS). RESULTS: Post-treatment CGI gains were generally maintained by MC-CBT patients at quarterly intervals through 12-month follow-up with negligible decay. For MC-CBT and S-CBT, 39 and 33% of respondents maintained treatment response at every follow-up assessment. The corresponding percent for EDU was 19%, which was significantly lower (p < 0.05) than for the CBT groups. On the IBS-SSS, therapeutic gains also showed a pattern of maintenance with trends towards increased efficacy over time in all conditions, with the mean unit reductions between baseline and follows-up being approximately -76 at immediate and approximately -94 at 12 months (-50 = clinically significant). CONCLUSIONS: For treatment-refractory IBS patients, home- and clinic-based CBT resulted in substantial and enduring relief of multiple IBS symptoms that generally extended to 12-month post treatment.