A 61-year-old man, with an 8-year history of ulcerative colitis, presented with bleeding per rectum for 4 weeks' duration. Colonoscopy revealed polypoidal neoplasm at the rectosigmoid junction. Histopathology depicted small cell carcinoma. On immunohistochemical staining, chromogranin A and synaptophysin were positive. The tumour was diagnosed as undifferentiated small cell carcinoma, which is unusual since generally it is the adenocarcinoma that occurs on a background of ulcerative colitis and there are only three previous reports of small cell carcinoma occurring in UC.