The principal prognostic factors for carcinomas which arise in the anal canal are similar to those of most other epithelial malignancies. The prognosis for survival deteriorates as the primary tumour enlarges and worsens as cancer metastasises to the regional lymph nodes and to extrapelvic sites. The relative rarity of anal canal carcinoma (incidence about 0.5–1 per 100 000) has meant that prognostic factors have, for the most part, been evaluated by univariate analysis in small groups of patients. Conflicting results have been common. More recently, larger series have been assembled and assessed by multivariate analysis or similar statistical techniques.