High-altitude sickness includes three conditions - acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE), which occur in mountaineer visiting high-altitude locations. Altitude sickness is due to hypobaric hypoxia and is not directly related to age or physical condition [6]. We present a case of a 32-year-old man, an alpinist who died while climbing Mont Blanc. A forensic medical autopsy was performed in Bulgaria to determine the cause of death. Autopsy and subsequent microscopic examination of the deceased's organs revealed High-altitude sickness, morphologically represented by pulmonary edema with bilateral confluent parenchymal hemorrhage (high-altitude pulmonary edema), and severe cerebral edema with hypoxic encephalopathy (high-altitude cerebral edema), as well as severe rheological disorders in the internal organs - focal subepicardial hemorrhages, small focal cortical hemorrhages in the kidneys; pronounced interstitial edema in the myocardium and renal medulla.