The increasing popularity of scuba diving has added a new category to the differential diagnosis of headache. Headache in divers, while uncommon and generally benign, can occasionally signify serious consequences of hyperbaric exposure such as arterial gas embolism, decompression sickness, and otic or paranasal sinus barotrauma. Inadequate ventilation of compressed gases can lead to carbon dioxide accumulation, cerebral vasodilatation, and headache. Other types of headache encountered in divers include exertional headache, cold stimulus headache, migraine, tension-type headache, acute traumatic headache, cervicogenic headache, carbon monoxide poisoning headache, and headache associated with envenomation. Correct diagnosis and appropriate treatment require a careful history and neurologic examination as well as an understanding of the unique physiologic stresses of the subaquatic environment.