Microscopic colitis (MC) is an inflammatory condition of the large bowel that is associated with chronic, nonbloody diarrhea. Colonoscopy usually demonstrates normal mucosa, while tissue biopsy reveals intraepithelial lymphocytes or a subepithelial collagen band. Although no specific antibody has been discovered, MC is associated with several autoimmune disorders such as celiac disease, Hashimoto's thyroiditis, and rheumatoid arthritis. There are only a small number of case reports documenting possible hereditary MC cases, but up to 12% of patients with MC have a family history of inflammatory bowel disease. Other associations include proton pump inhibitor use, cigarette smoking, HLA-DQ2/86, and possibly some gastrointestinal infections.