Pre-operative radiotherapy may induce radiation colitis and tumour regression. Histological evaluation of radiation colitis needs to be reproducible to assess disease progression. The severity of radiation colitis can be assessed and graded according to its histological features. Increased severity of disease appears to be associated with a higher degree of cellular atypia and a lesser eosinophilic infiltrate. The severity of histological changes does not appear to be associated with post-operative complications. Tumour regression is an interesting phenomenon, the histological grading of which is of prognostic importance. Patients treated with long course radiotherapoy appear to have more incidences of postoperative complications. However, these are though to be related to the degree of tumour regression rather than to the type of radiotherapy.