The long term prognosis for many children diagnosed with brain tumors and other malignancies has improved dramatically over the last decades and is expected to continue to rise as a result of improved treatment. The increased survival in pediatric oncology, however, has been associated with an increased recognition of neurobehavioral sequelae of cancer and its treatment. Current understanding of the incidence, pathogenesis, and natural history of these neurobehavioral abnormalities is limited and considerable individual variation in the presence and severity of these complications has been noted. Central nervous system (CNS) abnormalities associated with childhood cancer and its treatment have been demonstrated on at least three levels which may be interrelated: neurobehavioral abnormalities, brain imaging abnormalities, and neurotransmitter abnormalities.