The intrathecal chemotherapy with methotrexate and cytarabine arabinoside is used for the treatment and prophylaxis of the primary central nervous system lymphoma. The therapy may induce neurotoxicity including the cauda equina syndrome. We report a case of a 58-year-old man with the diffuse large B-cell lymphoma, who developed the cauda equina syndrome after the administration of intrathecal methotrexate and cytarabine arabinoside, as diagnosed by the electrodiagnostic, urodynamic, and radiologic approaches.