Methotrexate causes several biochemical changes that impact the nervous system. The neurotoxicity usually affects the cerebral white matter, causing a leukoencephalopathy that can be chronic and progressive with cognitive decline. A 15-year-old male developed olfactory seizures and behavioral abnormalities (hypersexuality, placidity, and memory disturbances) compatible with partial Klüver-Bucy syndrome after treatment for central nervous system leukemia with intraventricular methotrexate. A magnetic resonance imaging study revealed evidence of white matter disease affecting both temporal lobes. A brain biopsy revealed a necrotizing encephalopathy compatible with methotrexate-related white matter injury. It may be prudent to verify normal cerebrospinal fluid dynamics before the administration of intraventricular methotrexate in children with a history of central nervous system leukemia.