Gastrointestinal complications frequently occur in patients admitted to the intensive care unit. Of these, ulceration and bleeding related to stress-related mucosal disease (SRMD) can lengthen hospitalization and increase mortality. The purpose of this review is to discuss the many risk factors and underlying illnesses that have a role in the pathophysiology of SRMD and evaluate the evidence pertaining to SRMD prophylaxis in the intensive care unit population. Suppressing acid production is fundamental to preventing stress-related mucosal ulceration and clinically important gastrointestinal bleeding. Traditional prophylactic options for SRMD in critically ill patients include antacids, sucralfate, histamine 2 -receptor antagonists (H 2 RAs), and proton pump inhibitors. Many clinicians prescribe intermittent infusions of H 2 RAs for stress ulcer prophylaxis, a practice that has not been approved for this indication and may not provide the necessary degree or duration of acid suppression required to prevent stress ulcer-related bleeding. New data suggest that proton pump inhibitors suppress acid production more completely in critically ill patients, but more studies are required to assess their clinical effectiveness and safety for this indication. The prophylactic regimen chosen to prevent stress ulcer bleeding should take into account the risk factors and underlying disease state of individual patients to provide the best therapy to those most likely to benefit.