Abstract
A 67 year old man with myelodysplasia was admitted as an emergency with a six week history of rectal bleeding and diarrhoea. Barium enema showed an irregular polypoid filling defect in the lateral wall of the proximal rectum near the rectosigmoid junction. Histology showed this to be a granulocytic sarcoma (extramedullary granulocytic leukaemia; chloroma) infiltrating the bowel. A low index of suspicion of this lesion results in an incorrect diagnosis in many such cases. A chloroacetate esterase immunoperoxidase stain will confirm the granulocytic nature of the tumour cells.