The case of a 49 year old male patient who presented with perianal mucinous adenocarcinoma is presented. This is a rare anal tumour with a low grade, well-differentiated histological pattern. Its pathogenesis remains obscure, although a long antecedent history of fistula in ano and associated perianal sepsis is characteristic. The exact etiological relationship with anal fistula is not clearly established. The upper rectum is usually spared. Perianal Paget's disease is often seen in association with the tumour. Metastases occur late and spread is usually to the inguinal group of lymph nodes. Clinical diagnosis is often delayed and difficult. Treatment is abdominoperineal resection with block dissection of the inguinal lymph nodes if the glands are involved.