Neurotoxicity is a well-documented adverse effect of methotrexate in the treatment of pediatric cancers. The spectrum of symptoms is broad, can include stroke-like episodes and seizures, and classically resolves within days. The majority of patients tolerate subsequent doses without recurrence of symptoms. The population of patients who experience persistent and irreversible neurologic symptoms is poorly described, with the existing literature suggestive of a relationship with radiation therapy. The authors present a case series of 2 patients with pre-B-cell acute lymphoblastic leukemia who developed severe and ultimately fatal methotrexate-related neurotoxicity in the absence of radiation.