Carcinoma of the colon as a complication of chronic ulcerative colitis is relatively common, whereas malignant lymphoma is apparently rare. We report two cases of patients with malignant lymphoma complicating ulcerative colitis, a CD 30 + T-cell lymphoma of the intestine and a low grade B-cell non-Hodgkin’s lymphoma of MALT type. It is important to be aware of the possibility of malignant lymphoma in ulcerative colitis in order to evaluate correctly any lymphoid infiltrate seen in a biopsy, expecially when antiinflammatory treatment seems to be ineffective or when symptoms change.