A 56-year-old woman attended our hospital because of acute severe (thunderclap) headache. Neurological examination was normal and no abnormality was found on head CT or by cerebrospinal fluid examination. A few days later, she experienced a recurrence and suffered a seizure in her left upper and lower extremities. On neurological examination, she had conjugate deviation of the eyes toward the right side and left lower limb paralysis with Chaddock sign. MRI showed multiple hyperintense lesions in the bilateral occipital and parietal lobes, predominantly in the subcortical white matter at the right side on T2-weighted and FLAIR images. We diagnosed posterior reversible encephalopathy syndrome (PRES) because the ADC map showed a vasogenic edema pattern (increased ADC values in the hypodense lesions on diffusion-weighted image). Her blood pressure was normal and there were no underling diseases. As MRA showed vasoconstriction especially in bilateral posterior cerebral arteries, we initiated a therapy with a Ca-channel blocker. On follow-up MRI, the hyperintense lesions on T2-weighted and FLAIR images had almost disappeared, and vasoconstriction was also improved on MRA. This case suggested that cerebral vasoconstriction could underlie both thunderclap headache and PRES.