Type I antithrombin deficiency is an autosomal dominant disorder associated with high risk for venous thromboembolism. Data on the association between antithrombin deficiency and arterial thromboembolism are inconsistent. We report here the case of AT deficiency in a 43-year-old man free of cardiovascular risk factors who experienced venous thromboembolism and ischemic stroke followed by two transient ischemic attacks after interruption of oral anticoagulation due to colonoscopy. DNA sequencing of the antithrombin gene revealed heterozygosity for the previously reported substitution G to A at nucleotide position 9788 in intervening sequence four. To our knowledge, this report is the first to show that this genetic abnormality can be associated with recurrent cerebrovascular ischemic events.