A woman with a 7-year history of intermittent migraine had 3 months of gradually worsening headaches. Initial neurologic examination including fundus examination was normal, and initial head computerized tomographic (CT) scan and magnetic resonance imaging (MRI) were thought to be normal. The patient was given dihydroergotamine (DHE-45), 1.0 mg, intravenously for relief of headache. Five hours later, she complained of severe diffuse headache and nausea. Neurologic examination showed left arm weakness and sensory loss, blurring of the left optic disc, and bilateral Babinski signs. Cerebral arteriography demonstrated thrombosis of the sagittal sinus, which in retrospect was present on the initial contrast CT scan and MRI scan. The patient's deficits worsened, and she eventually died 20 days later as a result of cerebral infarctions and increased intracranial pressure, despite attempts at selective thrombolysis of the sagittal sinus. DHE has potent venoconstrictive effects. We suspect that DHE helped precipitate neurologic deterioration in this patient with sagittal sinus thrombosis.