Longstanding ulcerative colitis, particularly pancolitis, is associate
d with an increased risk of colorectal neoplasia. For this reason surv
eillance colonoscopy at regular intervals has been recommended to iden
tify early cancers or high grade dysplasia. Three cases are described
of patients with ulcerative colitis of greater than 10 years duration
who presented with colorectal carcinoma within three years of colonosc
opy.