Cancers of the anal canal are rare, accounting for approximately 1.5% of gastrointestinal tract malignancies. In the United States, there were an estimated 3400 new cases in 2000. In England, there were 245 new cases in men (1.0/100000) and 377 in women (1.5/100000) in 1997. It was originally thought that anal cancer was associated with chronic irritation from haemorrhoids, fissures, fistulae and inflammatory bowel disease. However, this is now known not to be so. The majority of anal cancers in both sexes are due to infection with human papilloma virus, particularly HPV1 6. There is an increased risk of anal cancer in men and women who practice anal receptive intercourse, who have had more than 10 sexual partners, or who have sexually transmitted diseases such as genital warts, gonorrhoea, or Chlamydia trachomatis. Other aetiological risk factors are immunosuppression, human immunodeficiency virus (HIV) infection, and smoking. Women with anal cancer have a higher incidence of vulval, vaginal, cervical and lung cancers.