We report the first case of cerebral venous thrombosis (CVT) diagnosed in an adult with Down's syndrome (DS). A 25-year-old man with DS was admitted because of a generalized tonic-clonic seizure and prolonged postictal period. Cerebral magnetic resonance imaging (MRI) and MR venography revealed CVT. No particular cause of the thrombosis was identified, CVT may be an unusual cause of stroke in DS. (C) 2001 Elsevier Science B.V. All rights reserved.