High-grade Non-Hodgkin's lymphomas are very aggressive type of malignancies. We report a high grade small B-cell (Burkitt's like) Non-Hodgkin's lymphoma that initially was considered and treated as ulcerative colitis without improvement or resolution of symptoms for nine months. The clinical presentation of 30 lb weight loss, diarrhea and dyspaurenia as complications of the developing and rapid growth of the mass were highly suggestive of malignancy. Acute lesions of ulcerative colitis begin at the anal verge and involve only the mucosa and submucosa. When induration of the perirectal areas develop a different pathology should be suspected.