The Chediak-Higashi syndrome (CHS) is a rare autosomal recessive immunodeficiency disorder. Some cases with CHS develop the accelerated phase characterized by pancytopenia, high fever and lymphohistiocytic infiltration of liver, spleen and lymph nodes. The treatment of the accelerated phase of CHS is difficult. We describe a case with CHS in the accelerated phase who had multiple polyposis and pulmonary infiltration that was probably due to involvement of CHS. She was successfully treated with high-dose methylprednisolone at her first admission. At her second admission, splenectomy was performed to remove hypersplenism, and her clinical, radiological and hematological findings improved significantly.