Intrathecal chemotherapy may be complicated with the development of myelopathies or toxic radiculopathies. This myeloradicular involvement, of toxic character, is unpredictable, since these patients have repeatedly received Intrathecal chemotherapy with the same drugs without apparent injury. The toxic effect should be mainly attributed to Cytarabine and not to methotrexate, since the central nervous system lacks Cytidine deaminase, the enzyme that degrades Cytarabine. We report two patients, an 18-year-old woman and a 16 years old male, who received systemic and intrathecal chemotherapy (methotrexate, cytarabine) for the treatment of an acute lymphoblastic leukemia and developed, in relation to this procedure, a spinal subacute combined degeneration. They had a proprioceptive and motor alteration of the lower extremities and neuroimaging showed selective rear and side spinal cord hyper intensity produced by central axonopathy. Two weeks later the woman developed a quadriplegia and the young man a flaccid paraplegia due to added root involvement.