A case of multifocal non-Hodgkin's (Diffuse large B cell type) lymphoma of colon in a patient with ulcerative colitis is described. The patient was a 69-year old male treated with azathioprine and methotrexate for ulcerative colitis for 2 years. He was admitted with loose stools and hematochezia. Colonoscopy revealed two deep ulcers in ascending colon and a large ulcer in rectum. Biopsy from both the sites revealed atypical large lymphoid cells, which were CD20 positive. A whole body PET-CT scan showed disease localized to colon with bone marrow examination showing no evidence of lymphoma. The patient was given chemotherapy cycles and recovered well.