This paper reports the case of a 16-year-old girl with acute lymphoblastic leukemia who received chemotherapy including intrathecal injections of methotrexate and preventive irradiation of the brain, but not of the spinal cord. Several months later, she died from an acute ascending poliomyelitic syndrome evolving during 10 days. Clinical, bacteriological, and viral investigations failed to demonstrate any pathological agent. Autopsy revealed an acute ischemic lesion involving both anterior horns of the whole spinal cord and extending from the lower segment up to the mesencephalic region, without significant alteration of the white matter. Neither tumoral invasion, nor vascular obstruction was found. The pathogenesis of this yet undescribed lesion remained unclear but a metabolic disorder seemed the most plausible pathological factor. © 1979 Springer-Verlag.