Autonomic dysreflexia is an acute syndrome of excessive, uncontrolled sympathetic output that can occur in patients who have had an injury to the spinal cord (generally at or above the sixth thoracic neurologic level). It is caused by spinal reflex mechanisms that remain intact despite the patient's injury, leading to hypertension. This review describes the clinical features of autonomic dysreflexia, its common causes (most frequently stimulation of the lower urinary tract) and a recommended approach to treatment. The condition can nearly always be managed successfully, but prompt recognition is essential--without treatment there may be dire consequences, including death.