Microscopic colitis is a common cause of chronic watery diarrhea that becomes more common as we age. Based on biopsy findings, 2 types of microscopic colitis are defined: collagenous and lymphocytic colitis. The clinical features of both are very similar. Patients typically present with chronic, watery, non-bloody diarrhea. Histologic changes define the 2 types of microscopic colitis. This presentation of symptoms often leads to evaluation for other types of inflammatory bowel disease, including Crohn disease and ulcerative colitis. The incidence has been increasing throughout northern Europe and northern North America, which is more common in women.