Hematemesis is regarded as an obvious sign of upper gastrointestinal bleeding (UGIB) as a result of the clinical manifestation of a pathologic disease process that indicates the presence of intraluminal hemorrhage anywhere from the oral cavity to the ligament of Treitz. It is a manifestation of overt gastrointestinal (GI) bleeding, as opposed to occult GI bleeding that does not manifest itself with external signs of hemorrhage and is usually referred to microscopic blood found in the stool. As a result, hematemesis typically demands emergency treatment algorithms that require protection of the airway, resuscitation with intravenous fluids, blood products, or both, in addition to endoscopic diagnostic and therapeutic maneuvers to treat the disease process after gastric decompression and lavage have been implemented. Hematemesis could be the result of a number of etiologies that ultimately necessitate prompt attention, a high index of suspicion, and especially resuscitation measures that may lead to referral to a surgical specialist for definitive treatment with therapeutic endoscopy or emergency surgical procedures. The recognition of hematemesis as a potential surgical emergency is essential for patient’s survival and for definitive management of the cause of the acute UGIB in a short amount of time and in compliance with resuscitation protocols. This chapter will illustrate the tenets of hematemesis diagnosis and management, including a practical surgical referral algorithm for primary care professionals who are exposed to this external manifestation of acute UGIB.