Autonomic dysreflexia is a poorly understood entity, typically occurring in the spinal cord-injured patient, with paroxysmal hypertension, bradycardia, severe throbbing headache, anxiety and sweating above the level of the lesion. An 18-year-old man underwent removal of a hemangioblastoma from the inferior portion of the fourth ventricle, a region known as the area postrema. Postoperatively he exhibited signs of autonomic failure. He later developed recurrent paroxysmal episodes of abdominal pain, hypertension, skin flushing and headaches. He subsequently was found to have a gastric ulcer. Symptoms and signs significantly improved with its treatment. We postulate that diminished sympathetic outflow occurred as a result of the surgery, creating a situation similar to the spinal cord-injured patient. Autonomic dysreflexia was elicited as a consequence of the noxious input of the gastric ulcer. In other cases of brainstem tumor resection, unrecognized episodes of autonomic dysreflexia may occur. This case also indicates that sympathetic supraspinal control is located at the level of the medulla or higher.