The risk of colorectal cancer is increased among patients with ulcerative colitis. The magnitude of this increase in risk and the effects of the length of follow-up, the extent of disease at diagnosis, and age at diagnosis vary substantially in different studies.

The rarity of colorectal cancer among young people is one reason for the increased standardized incidence ratio among those who were young at the time of diagnosis of ulcerative colitis, as compared with those who were older.

Close surveillance and perhaps even prophylactic proctocolectomy should be recommended for patients given a diagnosis of pancolitis, especially those who are less than 15 years of age at diagnosis.The excess cancers noted within two years after the diagnosis of colitis may have occurred in patients with long-lasting asymptomatic colitis that escaped diagnosis until a subsequent colorectal cancer caused symptoms.