Four cases of malignant histiocytosis of the intestine (MHI) are described in detail, with emphasis on the clinical features and laboratory findings that may lead to a diagnosis. MHI is a rapidly progressive, usually fatal condition, which may occur in a setting of adult celiac disease or apparently spontaneously; all patients, however, have villous atrophy and crypt hyperplasia of the jejunum. Characteristic symptoms are malaise, weight loss, abdominal pain, and diarrhea followed, after a period of weeks or months, by acute small intestinal obstruction, perforation, or bleeding. Because of the high mortality associated with MHI, suggestive symptomatology and investigations should, in the absence of a definitive diagnosis, lead to an urgent laparotomy with a view to chemotherapy if the diagnosis is made.