Severe hematochezia is a common reason for hospitalization but the causes have changed in the last decade. Changes are in part related to the aging population, the evaluation and treatment by colonoscopists rather than surgeons or non-endoscopists, and the changes in colonoscopic practices such as piecemeal polypectomy. A careful history, physical examination, rectal examination, and nasogastric lavage may help localize the bleeding site and focus the differential diagnosis. This should be routine while resuscitating the patient. However, purging the colon for urgent colonoscopy may be the most definitive way to combine diagnosis and treatment of bleeding colonic lesions. Complete colonoscopy with intubation of the terminal ileum is recommended, and also examination of the rectum with a slotted anoscope. If those examinations are negative, a push enteroscopy is recommended for combined diagnosis and treatment. With recent advances in colonoscopic hemostasis, patients will benefit from diagnosis and treatment by experienced colonoscopists. Also, urgent colonoscopy after purge has been reported to be more cost-effective than elective colonoscopy or other strategies for diagnosis of severe hematochezia.