Microscopic colitis describes a condition of chronic watery diarrhoea in the absence of macroscopic evidence of colonic inflammation but with characteristic microscopic appearances. It comprises the two separate but related conditions of lymphocytic and collagenous colitis. Disease severity ranges from mild and self-limiting to severe and refractory. Whereas mild disease can be managed adequately with loperamide, severe disease requires budesonide over the short term and, occasionally, immunomodulatory therapy with azathioprine.