Oculocephalic sympathetic functions were assessed in five patients with posttraumatic headaches using the thermoregulatory sweat test and biochemical pupillary responses. Four patients demonstrated bilateral sympathetic dysfunction following whiplash injury, and one patient demonstrated unilateral sympathetic dysfunction following forehead injury. Bio-chemical pupillary responses were diagnostic in the early posttraumatic period, while the thermoregulatory sweat test was abnormal up to 56 months following the injury. This study documents serious injury to the cervical sympathetic nerves in patients with posttraumatic headaches following whiplash injury, and shows the reliability of the thermoregulatory sweat test in identifying patients with long-term oculocephalic sympathetic dysfunction. It also shows dissociated postganglionic cranial sympathetic dysfunction. Our experience and a review of the pertinent literature shows no convincing clinical or experimental evidence to establish oculocephalic sympathetic dysfunction as a direct cause of head pain, but it may exert an effect on cephalic pain through the trigeminovascular system.