Objective. The case of a patient who developed a fatal post-exertional heat stroke is reported. Case Report. A 20-year-old man with a history of morbid obesity, hypertension, and schizophrenia was admitted to our intensive care unit because of multiorgan failure due to severe heat stroke. He had been working under the sun. Treatment included aggressive body cooling but, in spite of the best supportive care, the patient succumbed in a few hours. We concluded that the adverse event was possibly associated with his obesity and the use of antipsychotics. Histological evaluation revealed lesions consistent with severe hyperthermia and shock. Conclusions. Heat stroke is an uncommon clinical entity characterized by systemic heat and loss of the body's normal mechanisms for dealing with heat stress, such as sweating and temperature control. When heat stroke is diagnosed early and supportive care begins promptly the prognosis is optimal but it becomes a life-threatening disease when treatment is delayed. Lack of physical acclimatization and the use of certain medications that interfere with salt and water balance can impair thermoregulation under conditions of high environmental temperature. Health professionals must be adequately prepared to prevent, recognise, and treat them urgently.