Irritable bowel syndrome (IBS) has been reported in 10-22% of adults. Using a semistructured clinical interview to study the prevalence of IBS, we compared 31 patients seeking treatment for alcohol abuse or dependence in an outpatient setting with an age- and sex-matched control group of 40 patients who were seeking treatment in a general physician's office for other medical illnesses. The control group did not have any Axis I disorders. IBS was diagnosed according to the criteria of Drossman et al. Thirteen (41.9%) patients with alcohol abuse or dependence met the criteria for IBS, in contrast to 1 (2.5%) patient in the control group. We conclude that IBS is common and frequently underdiagnosed in patients with alcohol abuse or dependence.