Collagenous colitis is a rare cause of chronic watery diarrhea. No effective standard treatment has yet been established. Based upon anecdotal reports some anti-inflammatory and symptomatic drugs seem to have some therapeutic efficacy. Prednisone is widely believed to be the most effective treatment. Here we describe three female patients with histologically confirmed collagenous colitis refractory to therapy with prednisone. Each had received prednisone with a high starting bolus and lower dose maintenance therapy for their disease. However, definite clinical remission could not be achieved. After the administration of 3 x 3 mg/day controlled ileal release (CIR) capsules of budesonide the symptoms resolved immediately. The mean follow-up after beginning budesonide was 11 months (range 7-18). Two patients are still on budesonide. One had had a quick relapse of diarrhea after stopping her treatment. Budesonide therapy was therefore resumed. She has remained symptom-free on a lower daily dose of 2 x 3 mg/day budesonide. One patient has been in remission for more than 1 year after a 3-month course of budesonide. Budesonide is a topically acting steroid with rapid absorption, high receptor affinity, and low systemic bioavailability, thus causing almost no side effects. As yet only few case reports have been published on the use of budesonide for collagenous colitis. We present here the first three cases of prednisone refractory collagenous colitis successfully treated with budesonide.