Collagenous colitis is characterized clinically by chronic watery diarrhea and pathologically by a distinctive band of collagen deposited below the colonic epithelium and an inflammatory cell infiltrate of the lamina propria. Since 1976, more than 100 cases have been described. We report an additional nine cases occurring in five women and four men ranging in age from 18 to 80 years. Diarrhea was present before diagnosis for 2 to 4 months in four cases and for 1 to 25 years in another four cases. One patient did not have diarrhea. Results of radiologic and stool studies were normal in all cases. All patients had flexible sigmoidoscopy or colonoscopy. Microscopic examination of biopsy material was interpreted as characteristic of collagenous colitis. Two cases resolved with psyllium mucilloid therapy alone. Of the five patients treated with azulfidine, three had marked improvement, one had partial response, and one had no change.