Microscopic colitis (MC) is a chronic condition that is a common cause of watery diarrhea, particularly in the elderly. The etiology is unknown but widely considered to be an abnormal immune reaction to luminal antigens in predisposed hosts. Drugs and autoimmunity have also been implicated. The aims of the study are: 1) To quantitatively classify microscopic colitis using image analysis microscopy to determine whether the degree of lymphocytic infiltration correlates with etiology, symptoms and prognosis. 2) To investigate the etiology of microscopic colitis by examining medical and lifestyle risk factors including medications, autoimmunity, diet, and smoking 3) To evaluate the association between the adherent microbial flora and MC to assess whether bacterial dysbiosis is linked to presence of MC. As an exploratory aim we will evaluate whether CYP2C19 polymorphisms are more common in purportedly drug-induced disease since the diverse drugs that have been associated with MC are all substrates for this gene.