Cancer is often preceded by dysplasia in both patients with ulcerative colitis and in patients with Crohn's disease affection. Young patients who have severe Crohn's disease of long standing, with extensive colonic involvement may benefit from endoscopic surveillance for cancer, especially those affecting the large intestine. We’re waiting for good screening methods more sensitive, less invasive and less costly in terms of economic cost and discomfort for the patient. An attitude of alertness may be stated as good: the onset of new symptoms in a patient with up till now stable disease should always be investigated.