Ulcerative colitis: A bowel disease that is characterized by inflammation with ulcer formation in the lining of colon (large intestine). Its cause is unknown. The end of the colon (the rectum) is generally involved. When limited to the rectum, the disease is called ulcerative proctitis. The inflammation may extend to varying degrees into the upper parts of the colon. When the entire colon is involved, it is referred to as pancolitis or universal colitis. Symptoms include intermittent rectal bleeding, crampy abdominal pain, and diarrhea. Many patients experience long remissions, even without medication. Ulcerative colitis may mysteriously resolve after a long history of symptoms. Direct visualization (via sigmoidoscopy or colonoscopy) and biopsy of the lining of the bowel is the most accurate diagnostic test. Treatment of ulcerative colitis involves medications and/or surgery; changes in diet can sometimes help.