We randomized, at two sites, 210 patients with Rome II diagnosed irritable bowel syndrome (IBS), of at least moderate severity, to one of three conditions: group-based cognitive therapy (CT; n=120), psychoeducational support groups (n=46) as an active control, or intensive symptom and daily stress monitoring (n=44). One hundred eighty-eight participants completed the initial treatment. Those in symptom monitoring were then crossed over to CT. For an intent to treat analysis on a composite GI symptom measure derived from daily symptom diaries, both CT and the psychoeducational support groups were significantly more improved than those in the intensive symptom monitoring condition, but the CT and psychoeducational support group did not differ. Among treatment completers on the same composite measure of GI symptoms, again, both CT and psychoeducational support groups were statistically superior to symptom monitoring but did not differ on the symptom composite, or on any other measure. On individual IBS symptoms, both CT and psychoeducational support were statistically superior to symptom monitoring on reductions in abdominal pain and tenderness and for flatulence. Patient global ratings at the end of treatment showed the two active conditions statistically superior to symptom monitoring on change in Bowel Regularity, with CT superior to symptom monitoring on reduction in overall pain and in improvement in sense of well-being. Three-month follow-up data on 175 patients revealed maintenance of significant improvement or continued significant improvement on all IBS symptoms, including the McGill Pain Questionnaire. Group CT and psychoeducational support groups continued not to differ on any measure. We thus conclude that group CT is not superior to an attention placebo control condition.