Heat stroke is a life-threatening cause of hyperthermia and altered mental status. Cardinal symptoms include a temperature above 40°C (104°F), neurologic dysfunction, and anhidrosis. Patients with heat stroke experience a variety of neurological abnormalities including ataxia, seizure, and hallucinations. It is caused by the body's inability to fully dissipate heat. It often occurs in the setting of high environmental temperature and physical exertion. Other factors, such as certain medications, medical conditions, and dehydration, may make a person more prone to heat stroke.

Meningitis, neuroleptic malignant syndrome, toxic ingestion, and other conditions may mimic heat stroke, so the diagnosis must carefully consider clinical history. Treatment primarily consists of physical cooling (evaporative, ice water, etc), fluid resuscitation, and monitoring for complications.