Ulcerative colitis (UC) is a disease in which chronic inflammation of the colon leads to diarrhea, bleeding into the stool, abdominal pain, difficulties with nutrition, and an increased risk for colon cancer. Primary sclerosing cholangitis (PSC) is an inflammatory disease of the biliary tract, the system that brings bile from the liver to the gut. Approximately 2% to 4% of patients with UC also have PSC. Nearly half of patients with both UC and PSC will develop colon cancer or precancerous changes of the colon (dysplasia) within 25 years of diagnosis of UC. This risk for cancer is so high that some patients are willing to have their colons removed surgically as a preventive measure. Strategies to decrease the risk for colon cancer, other than removal of the colon, could benefit patients with both UC and PSC. Ursodiol is a drug that has been useful in treating liver abnormalities in patients with PSC. Ursodiol decreases the amount of bile acids that reach the colon; this is important because bile acids may play a role in the development of colon cancer.