Intracranial hemorrhage during blastic crisis is a rare but critically important occurrence in children with acute lymphoblastic leukemia. This form of hemorrhage has not been described since the advent of magnetic resonance imaging (MRI), leaving radiologists and clinicians unfamiliar with its unique imaging features. The authors describe 2 boys with severe intracranial pathology secondary to blastic hyperleukocytosis. Both patients were followed with serial MRI. Imaging findings in relation to the pathophysiology of white matter leukostasis are discussed and implications for treatment and prognosis are considered.