Microscopic colitis is currently classified as a chronic inflammatory bowel disorder and encompasses two entities: lymphocytic colitis and collagenous colitis. Patients with microscopic colitis present with a well-tolerated chronic watery diarrhea, sometimes with abdominal pain. Colonoscopy is normal. Diagnosis of microscopic colitis is established by histologic examination of colonic biopsies, showing a thickened subsurface collagen band higher than 10 microm in collagenous colitis, and an increased number of surface intra-epithelial lymphocytes higher than 20 lymphocytes per 100 epithelial cells in lymphocytic colitis. Causes of microscopic colitis are still unknown, although a drug-induced etiology is found in some cases. Patients are usually treated with budesonide but recurrences are frequent.