We surveyed all patients with collagenous colitis seen at Johns Hopkins over a 4-year period, using a standardized, previously validated telephone questionnaire. Of 29 patients, 2(7%), including the index case, had monoarticular reactive arthritis. Five additional patients (17%) had a coexisting autoimmune illness. Collagenous colitis should be added to the list of causes of enteropathic arthritis. In addition, collagenous colitis should be considered in the differential diagnosis of diarrhea occurring in patients with known autoimmune diseases.