An 80-year-old man, presenting with gait disturbance and memory loss, had findings of normal pressure hydrocephalus. Primary leptomeningeal lymphoma (PLML) was diagnosed based on cytology and flow cytometry of cerebrospinal fluid obtained by examination. Gadolinium-enhanced MRI showed enhancement of the brain and spinal cord but FDG-PET/CT revealed no lymph node swelling. With intrathecal chemotherapy, meningeal lesions disappeared and the gait disturbance and memory loss improved. However, the disease recurred three months later, manifesting as left facial nerve palsy, but the symptoms disappeared in response to intrathecal chemotherapy and systemic rituximab administration. Although a tumor lesion in the spinal canal was suggested by MRI examination, the patient has maintained a good clinical course for four years with intrathecal chemotherapy every three months. PLML is a very rare disease and its diagnosis is difficult. Repeated intrathecal chemotherapy appeared to be effective against PLML in this case.