Heat stroke is a life-threatening and often fatal medical emergency. Key symptoms include fever exceeding 40°C and neurological deficits. In heat stroke thermoregulation mechanisms become inefficient and the body is unable to maintain its normal temperature. Ineffective thermoregulation results in elevation of body temperature to extreme values, leading to multiorgan failure and sometimes even to death. Most at-risk of developing heat stroke are infants and the elderly. Other risk factors include intense physical exertion at high ambient temperature and humidity, dehydration and some drugs. Heat stroke occurring in adolescents and adults as a result of intense physical effort is classified as exertional heat stroke. The incidence of exertional heat stroke during long-distance running mass events is estimated at 1 per 1000. Taking into account increasing popularity of long-distance running in Poland, the chance of facing such events by health professionals will be increasing. Timely diagnosis and effective management of heat stroke are paramount for the patients’ survival and long-term prognosis. Standard treatment of heat stroke includes rapid cooling in order to reduce deep temperature below critical threshold value of 40°C and correction of water-electrolyte disturbances. Medical services supporting mass events should be adequately prepared to deal with such cases. This paper presents a case of a 39-year-old marathon runner,who developed an exertional heat stroke with associated focal neurological deficits and indices of multiorgan failure persisting for several days after onset of heat stroke. Clinical picture of exertional heat stroke, associated risk factors and recommended management are discussed.