Posterior reversible encephalopathy syndrome (PRES) is a condition characterized by symptoms including headache, seizures, visual disturbances, altered mental function, and abnormal neuroimagings in the posterior regions of the cerebral hemispheres. PRES is named as reversible but not always reversible. A 6-year-old girl undergoing combined chemotherapy with cyclosporine A and prednisolone for the treatment of hemophagocytic syndrome (HPS) developed hypertention and coma. She was diagnosed with PRES by brain MRI. We stopped using immunosuppressive agents and gave nifedipine to lower her blood pressure but, on the 3rd ICU day, we resumed them to treat relasped HPS. We controlled her blood pressure by continuous intravenous nicardipine to prevent PRES and the patient has recovered completely in clinical signs in the 4th ICU day and in radiological findings at a later time. So far as we search this is the first case of PRES resulting from HPS.