A 68-year-old woman presented with thunderclap headache, which led to a search for subarachnoid hemorrhage. Both computerized tomography of the head and cerebrospinal fluid examination were normal. Magnetic resonance imaging revealed abnormalities in the white matter in the parieto-occipital regions. There was no aneurysm on magnetic resonance angiography. Treatment of hypertension led to resolution of the posterior leukoencephalopathy. Hypertensive encephalopathy with reversible posterior leukoencephalopathy can present as a thunderclap headache.