This research is based on previously obtained findings that CNS treatment of patients with acute lymphocytic leukemia (ALL) had the delayed effect of producing a deficit in intellectual functioning that appears to be somewhat progressive and is greater among children treated at a younger age. The current research involves comparing children who receive either the standard CNS treatment or an alternative non-CNS treatment. All patients are tested on a series of neuropsychological measures dealing with short and long term memory, attention, perceptual-motor functioning, coordination, concept formation, academic skills, and general cognitive functioning. These children are studied longitudinally and are assessed several times over a five to seven year period. The purpose of the assessments is to determine if the non-CNS treatment is less neurotoxic and results in more or less neuropsychological deficits than the standard CNS treatment.