OBJECTIVE: In the nearly 20 yr since collagenous colitis was first recognized, the results of therapies have not been systematically described in substantial numbers of patients. We have therefore conducted a retrospective analysis of 26 patients treated in this institution during the years 1991-1994. METHODS: Twenty-nine cases of collagenous colitis were obtained by review of biopsy specimens collected between 1991 and 1994 at The Mount Sinai Hospital. Each chart was reviewed for patient demographics, symptoms, coexisting conditions, specific therapies, and therapeutic outcomes. Additional data were obtained from telephone calls to patients when deemed necessary. Three patients were excluded from the study because of lack of follow-up. Therapeutic outcomes were defined as follows: Complete Remission (CR): normalization of bowel function; Partial Remission (PR): 50% reduction in frequency of bowel movements; Failure: <50% reduction in frequency of bowel movements; or Relapse: return of symptoms after cessation of treatment. Median follow-up was 58 wk from time of diagnosis, with a range of 22-376 wk. RESULTS: The 26 patients (25 women, one man) had a mean age of 62 yr (range, 22-85 yr) at diagnosis. Of 26 patients, 22 responded to some form of therapy and one had spontaneous remission. Six of the responders ultimately remained in CR with no therapy. Twelve are maintained on 5-aminosalicylic acid (5-ASA) and or antidiarrheals to control symptoms. An additional six required prednisone throughout the follow-up period to remain in CR or PR. Two patients failed all therapy. CONCLUSION: Collagenous colitis is a treatable condition in most patients. We recommend initial therapy with antidiarrheals, followed by a trial of 5-ASA agent. A trial of 5-ASA in combination with prednisone should be attempted in patients refractory to 5-ASA alone, with subsequent attempts in the responders to taper prednisone and maintain remission with no therapy, if possible, or with 5-ASA and/or antidiarrheal agents if necessary.