Acute leukemia in children may present with hyperleukocytosis. Symptomatic hyperleukocytosis is a medical emergency that necessitates rapid stabilization of the patient and prompt lowering of the leukocyte count. We report on a patient with intracranial hemorrhage associated with T-cell acute lymphoblastic leukemia with hyperleukocytosis, which is a rare occurrence. A 16-year-old boy with hyperleukocytosis (total white cell count; 398x10(3)/mu L) underwent repeated leukapheresis and received supportive treatment until a definite diagnosis of T-cell acute lymphoblastic leukemia was made and chemotherapy was started at 10% of the usual dose. On day 2 of treatment, he had headache, vomiting, and was agitated. Brain magnetic resonance imaging showed bilateral extensive hemispheric and cerebellar punctate areas of hemorrhage and perilesional edema. Chemotherapy intensified to a maximum dose on day 3. If supportive care for tumor lysis syndrome can be promptly provided, initial chemotherapy regimen can immediately be begun at an optimal dose.