There may be considerable difficulty in making a definitive diagnosis in colitis from histopathology alone. This study is based on a well-tried system which has been used for 15 years in the University Hospital of South Manchester for the reporting of colonic biopsies. The varieties of histopathological pattern seen in colitis are described and the study shows how they can be used to refine diagnosis when good communication is maintained between the clinician and the histopathologist. The histopathology report is based on describing histological patterns rather than diagnoses but includes a differential diagnosis. The pathology report will allow the clinician together with the known clinical information to make an appropriate management decision. Ideally the final diagnosis is reached at a clinico-pathological conference.