One hundred cases of upper gastrointestinal hemorrhage in peruvian highlanders were studied at a hospital in La Oroya (3850 meters above the sea level). On admission in all of them an esophagogastroduodenal fiberscope was performed to establish the diagnosis. Most of them were males (98%), between 30-39 years of age (38%) and presented at the same time hematemesis and melena (64%). After bleeding in 72% the hemoglobin was over 14 g%. As a whole the most frequent diagnosis were: gastric ulcer (33%). duodenal ulcer (23%) and erosive gastritis (23%). In those living between 3000-3500 m.a.s.l. duodenal ulcer had the highest incidence. At 3500 m.a.s.l. was gastric ulcer more frequent, followed by erosive gastritis. In 11% surgery was required and only in 27% it was necessary a blood transfusion. After bleeding 10% had an hemoglobin level over 20 g% and because of this they were considered as having Chronic Mountain Sickness, 4 of them with severe cardiorespiratory and consciousness disturbances required after the gastrointestinal hemorrhage, an immediate bleeding in order to compensate the patient, a completely unusual occurrence in general pathology but a peculiar treatment in these patients living at high altitudes of the peruvian Andes.