Other intestinal conditions can cause symptoms similar to ulcerative colitis, including:

• Diverticulitis, which is inflammation or infection of pouches (diverticula) that form in the wall of the large intestine (colon).
• Colorectal cancer, which is the abnormal growth of cancer cells in the muscular tube that makes up the lower digestive tract (large intestine).
• Irritable bowel syndrome, which is a common digestive problem that causes episodes of abdominal pain, cramping or bloating, and diarrhea or constipation.
• Lactose intolerance, in which a person is not able to digest lactose, a natural sugar generally found in cow's milk–based foods.
• Intestinal abscess, which is a pocket of pus that forms at the site of infected tissue in the intestine.
• Hemorrhoids, which are enlarged, swollen veins in the anus. Hemorrhoids may bleed, but they do not cause abdominal pain and cramping.

Other forms of colitis that can be confused with ulcerative colitis include:

• Ischemic colitis. This painful condition occurs suddenly because of loss of blood supply to a part of the colon. It can cause bloody diarrhea.
• Infectious colitis. Various bacteria can cause infection that irritates the colon. The cause sometimes can be identified with a stool sample.
• Collagenous colitis. The main symptoms are watery diarrhea and crampy abdominal pain. The cause is not known.
• Lymphocytic or microscopic colitis. This form of colitis has symptoms similar to collagenous colitis and must be identified using a microscope.
• Amebic colitis. Travelers to areas with amebic diseases may develop inflammation, pain, and bloody diarrhea.