RESUMEN
Paroxysmal sympathetic hyperactivity may appear after brain injury. Its clinical manifestations are sporadic and self-limited crisis of arterial hypertension, hyperthermia, tachycardia, hyperhidrosis, muscle tension, sialorrhea and mydriasis. These subside with the administration of morphine and beta-blockers. It may be caused by a dysautonomia leading to increased levels of catecholamines due to the lack of brain regulation. We report a 19 years-old man with a history of illicit drug and alcohol consumption, with a secondary axonal injury due to a cranioencephalic trauma. During hospitalization, he had recurrent, self-limited episodes of dysautonomia. An infectious cause was discarded. When morphine was administrated suspecting the presence of pain, the crisis subsided, which helped to establish the diagnosis of paroxysmal sympathetic hyperactivity.