Colorectal cancer (CRC) is common, affecting >40,000 people a year in the UK. Most cancers are sporadic but a few, such as those occurring at a younger age, have a clear genetic basis. Most are situated in the rectum or rectosigmoid and cause rectal bleeding, often with a looser or more frequent stool. Right-sided cancers typically result in anaemia, because the blood in the stool is occult and unnoticed by the patient. Almost all symptoms of malignancy can also be caused by benign disease. Diagnosis relies on luminal imaging, with colonoscopy being the gold standard.