Cortical hyperexcitability is thought to explain the more enhanced contingent negative variation (CNV) amplitudes and impaired CNV habituation that have been found during the interictal period in migraine without aura. These CNV characteristics have been shown to normalize to the level of healthy controls during an attack. This study aimed to replicate the interictal findings, and additionally examine whether migraineurs show reduced CNV amplitudes during the postattack period. Of 12 patients with migraine without aura and their sex- and age-matched healthy controls, CNV characteristics were recorded once in an interictal period, once during the postattack period within 30 hours after an attack that was treated with sumatriptan, and once after an attack that was treated with habitual nonvasoactive medication (counterbalanced). The present results did not confirm the enhanced CNV early and late wave amplitudes or impaired habituation, and cortical hyperexcitability that have previously been reported in the interictal period in patients with migraine without aura. During the postattack period, a decrease in CNV early and late amplitudes was found but only after sumatriptan use. This reduction in CNV amplitudes was most prominent over the frontal cortex and could reflect cortical hypoexcitability, possibly related to a suppression of central catecholaminergic activity by sumatriptan.