We describe four patients with acute esophageal necrosis who were admitted to hospital due to upper gastrointestinal bleeding. "Black esophagus" is endoscopically defined as diffuse dark pigmentation of the esophageal wall. The underlying conditions were ketoacidosis in three of the patients and diabetes mellitus in two. Three patients responded well to empirical supportive therapy and one patient died of coexisting illness rather than the esophageal status. Acute esophageal necrosis is a rare entity that should be considered in the differential diagnosis of upper gastrointestinal bleeding.