We describe a case with unilateral chorea associated with thyrotoxicosis. A 23-year-old female with no family history of neurological diseases acutely developed choreic movements of the left extremities during gross thyrotoxicosis. CT scan and MRI study demonstrated no abnormality. Single-photon emission CT with technetium Tc 99m-labeled hexamethylpropyleneamine oxime revealed normal cerebral perfusion. Although the choreic movements were partially improved by dopamine antagonist, they persisted for two months until successful treatment of the thyrotoxicosis finally abolished these movements. Increased sensitivity of dopamine receptors may be responsible for persistent choreic movements in thyrotoxicosis.