Early diagnosis is most important in the prognosis in colorectal cancer because the cause of cancer is unknown and an effective and practical large‐scale screening test, easily and cheaply carried out, is unavailable. If the diagnosis is made early, when the patient is asymptomatic, and prior to development of complications or when the lesion is precancerous, the disease almost always is localized and adequate treatment gives excellent results. However, if symptoms have been present for months or complications have developed prior to establishing the diagnosis (because of patient neglect in seeking advice or physician lack of tenacity in evaluating the patient's condition), or if surgical treatment has been inadequate, the prognosis is poor. Education of physicians and the public remains most important in improving results further. New knowledge or new modalities of treatment should result in improved prognosis not only in colorectal cancer but also in cancer of other anatomic sites.