OBJECTIVES: This prospective, randomized controlled trial explored the feasibility and efficacy of a group program of mindfulness training, a cognitive-behavioral technique, for women with irritable bowel syndrome (IBS). The technique involves training in intentionally attending to present-moment experience and non-judgmental awareness of body sensations and emotions. METHODS: Seventy-five female IBS patients were randomly assigned to eight weekly and one half-day intensive sessions of either mindfulness group (MG) training or a support group (SG). Participants completed the IBS severity scale (primary outcome), IBS-quality of life, brief symptom inventory-18, visceral sensitivity index, treatment credibility scale, and five-facet mindfulness questionnaire before and after treatment and at 3-month follow-up. RESULTS: Women in the MG showed greater reductions in IBS symptom severity immediately after training (26.4% vs. 6.2% reduction; P=0.006) and at 3-month follow-up (38.2% vs. 11.8%; P=0.001) relative to SG. Changes in quality of life, psychological distress, and visceral anxiety were not significantly different between groups immediately after treatment, but evidenced significantly greater improvements in the MG than in the SG at the 3-month follow-up. Mindfulness scores increased significantly more in the MG after treatment, confirming effective learning of mindfulness skills. Participants' ratings of the credibility of their assigned interventions, measured after the first group session, were not different between groups. CONCLUSIONS: This randomized controlled trial demonstrated that mindfulness training has a substantial therapeutic effect on bowel symptom severity, improves health-related quality of life, and reduces distress. The beneficial effects persist for at least 3 months after group training.