We report a 54-year-old female patient in whom thyroid storm was improved dramatically by plasma exchange. The patient presented with tachycardia, high fever and pulmonary congestion, in addition to left hemiparalysis and dysarthria. Serum thyroid hormone concentrations were markedly increased and computed tomography showed a fresh cerebral infarct, suggesting that she had thyroid storm precipitated by cerebral infarction. As there was no remarkable improvement even after 24 h of conventional therapy, plasma exchange was carried out using fresh frozen plasma. Consequently, her critical condition improved quickly. The half-life of thyroid hormones is so long that quick improvement is not always achieved even by sufficient doses of antithyroid drugs. Thus, plasma exchange in combination with conventional therapy appears to be effective in relieving the life-threatening state in our patient with thyroid storm precipitated by acute cerebral infarction.