Thunderclap headache (TCH) is a sudden severe headache that peaks to maximum intensity within 1 minute. Subarachnoid hemorrhage is the most commonly identified etiology for this headache, however, other secondary etiologies should be considered. Sentinel headache, reversible cerebral vasoconstriction syndrome, arterial dissection, cerebral venous sinus thrombosis, pituitary apoplexy, intracranial hemorrhage, ischemic stroke, reversible posterior leukoencephalopathy, spontaneous intracranial hypotension, colloid cyst, and intracranial infections are other possible causes of TCH. Investigations for the etiology of TCH begin with noncontrast CT head and lumbar puncture. MR brain, CT angiogram, MR angiogram, or CT/MR venogram may need to be performed if the initial investigations are negative. Treatment and prognosis depend on the etiology of the TCH.