Inflammation of the mucous membranes lining the small intestine. Symptoms include nausea, vomiting, abdominal pain and cramping, frequent bowel movements, watery or bloody diarrhea, fatty stools and weight loss.

Enteritis may be caused by disease, certain drugs or radiation therapy. When enteritis is caused by radiation to the abdomen, pelvis or rectum, it is called radiation enteritis (or radiation enteropathy).