Risk factors of children with arterial ischemic stroke were retrospectively evaluated. The children were grouped according to values on developing diagnostic tools: 13 in the old era (1987-1994) and 18 in the new era (1995-2004). The old era battery included 5 tests: protein C, protein S, antithrombin, lupus anticoagulants, and anticardiolipin antibodies. The new era battery added 5 more tests: homocystine level, factor VIII level, mutations for factor V Leiden and prothrombin G20210A, and lipoprotein (a) level. At least 1 risk factor was found in 5 of 13 children (38.5%) in the old era and in 8 of 18 (44.4%) in the new era. The extended battery for prothrombotic disorders revealed 7 risk factors in 4 children (22.2%) in the new era, whereas the limited battery identified a single risk factor in 1 child (7.7%) in the old era. For the correct etiologic identification, prothrombotic risk factors should be extensively evaluated in patients with arterial ischemic stroke.