Ninety children were treated for acute lymphoblastic leukemia or non-Hodgkin lymphoma during 1986 through 1992 in the Children's Hospital, University of Helsinki, in Finland. During induction chemotherapy, nine of the children had visual hallucinations progressing to confusion and seizure. The symptoms were often preceded by severe constipation and significantly elevated blood pressure. Neuroradiologic examinations showed bilateral cortical or subcortical white matter lesions. Despite the stroke like manifestations, the lesions were reversible. The triangular shape and location of the lesions in the watershed areas between the major cerebral arteries suggest vascular ischemia as the cause.