During or immediately following L-asparaginase (L-asp) therapy especially intracranial thromboembolic or hemorrhagic complications due to hemostatic imbalance have been observed. We report about 6 children who had intracranial thrombosis or hemorrhage after 3 to 8 doses of L-asp. Initial symptoms of the cerebral events were similar--seizure, coma, hemiparesis and disorientation. All patients were examined by cerebral computerized tomography (CT) or/and magnetic resonance imaging (MRI). Three patients had a dural sinus thrombosis, one had an intracranial hemorrhage and two a hemorrhagic infarction with typical findings in the cerebral CT or MRI. Two other patients were interpreted as having peripheral thrombosis. They showed nontypical hypodense cortical and subcortical areas without any contrast medium enhancement in CT and hyperintense areas in T2-weighted MRI scan. All patients recovered from neurological symptoms, and showed obvious regression of CT and MRI findings which correlate with the good prognosis of these complications. Both CT and MRI are useful in diagnosis and follow-up of cerebrovascular complications of L-asp therapy. The CT and MRI findings of the reported cases seem to reflect different appearances of the same entity, i.e. thrombosis of venous vessels of different size with or without congestive edema and hemorrhagic complication.