In childhood, the conus medullaris syndrome owing to leukemia is rare. Here, a 12-year-old boy with acute myeloblastic leukemia, maxillary mass, and conus medullaris syndrome is reported. A biopsy from the maxillary mass revealed “granulocytic sarcoma.” Lumbosacral magnetic resonance imaging revealed clumped and thickened cauda equina nerve roots, epidural and periradicular diffuse soft tissue, which was enhanced with gadolinium. Cerebrospinal fluid revealed elevated protein but no cells. Chemotherapy and local radiotherapy for both the face and the spine, yielded bone marrow remission and abatement in neurologic and radiologic findings, but he developed bone marrow relapse and died because of sepsis.