OBJECTIVE: To describe microscopic colitis (MC) and a stepwise approach to its diagnosis and management. QUALITY OF EVIDENCE: MEDLINE was searched from January 1996 to August 2002. Controlled trials were sought, but due to their relative rarity, most articles cited are well designed retrospective studies and reviews. MAIN MESSAGE: Microscopic colitis in both its collagenous and lymphocytic forms is a relatively common and important cause of diarrhea in middle-aged and elderly patients. It usually presents as chronic watery diarrhea. Results of endoscopic and radiologic examinations are normal; specific histologic findings are seen on colonic biopsy. Once the diagnosis is confirmed, we suggest a stepwise approach to therapy. First-line therapies include antidiarrheal agents; second-line include bismuth subsalicylates and budesonide; third-line include cholestyramine and 5-aminosalicylic acid agents. When patients fail to respond to these therapies, oral corticosteroids or immune modulatory therapy should be considered. For severe unresponsive cases, colectomy is the last resort. CONCLUSION: Microscopic colitis is an important cause of chronic diarrhea. Once the diagnosis is confirmed, a stepwise approach to treatment is suggested.