Cognitive behavioural therapy (CBT) can reduce IBS symptom scores; however, the current availability of this therapy is poor and uncertainty exists in its long-term effectiveness and optimum mode of delivery. In a randomized controlled trial in primary and secondary care conducted in the South of England, the clinical effectiveness of telephone-delivered CBT (TCBT) and web-delivered CBT (WCBT) for IBS were compared with treatment as usual (TAU). Out of 1,452 patients with refractory IBS screened for eligibility, 558 were allocated to one of the three treatment groups. After 12 months follow-up, the co-primary outcomes of IBS Symptom Severity Score and Work and Social Adjustment Score were both significantly decreased (P ≤ 0.002) in the groups receiving TCBT and WCBT compared with TAU. The trial shows that sustained improvements to IBS symptoms can be achieved with remotely delivered therapies that could increase CBT availability in isolated or resource-poor locations.