Complications of endoscopy in patients with gastrointestinal (GI) bleeding may result from patient- and procedure-related factors. Cardiopulmonary complications occur as a result of the sedation used, comorbid illnesses, and type of endoscopic procedure performed. As GI bleeding is a potentially life-threatening emergency, endoscopic procedures often need to be performed in patients with other acute illnesses, including acute myocardial infarction. Although endoscopy usually can be performed safely in this setting, high-risk criteria identify patients at increased risk for complications. In patients at high risk of aspiration, such as those with altered mental status or with massive upper GI bleeding, elective endotracheal intubation is recommended. In addition to patient-related factors, procedural risks depend on the site of bleeding, source of bleeding, and type of endoscopic intervention used. Specific techniques of endoscopic hemostasis are associated with certain complications, but treatment-specific precautions may be taken to reduce complications. Attention to endoscopic technique and patient factors is needed to minimize risk during endoscopic treatment of hemorrhage.