A rare case of cerebral venous thrombosis associated with thrombocythemia is reported. A 47-year-old man presented with headache, papilledema, and diplopia. Complete blood count showed an increased number of platelets. MR images and venography showed the thrombosis from the superior sagittal sinus (SSS) to the bilateral transverse sinuses (TS). The patient was treated with thrombolysis, continuous heparin infusion, and oral warfarin. On day 2, angiography demonstrated partial recanalization of the SSS and the left TS. Since CSF pressure was 30 cmH2O at day 11, a spinal drainage catheter was installed. Nevertheless, the patient presented with left hemiparesis, seizure, and loss of consciousness on day 12. Angiography revealed thrombosis from the SSS to the left TS and the right sigmoid sinus. Mechanical thrombolysis with a balloon was performed, and partial recanalization was obtained. In order to control the intracranial pressure, barbiturate coma therapy was performed for 1 week. On day 19 aspirin therapy was initiated become of continuous thrombocythemia. On day 25, the patient recovered completely. This case suggests that thrombocythemia may be able to cause refractory cerebral venous thrombosis.