The Chediak-Higashi syndrome (CHS) is a rare, autosomal-recessively inherited disease characterized by giant cytoplasmic granules in neutrophils, monocytes and lymphocytes. It has been reported that a lymphoma-like illness develops in the accelerated phase of the syndrome and that early death ensues. Treatment of CHS has not been established, particularly when the accelerated phase develops. We treated a 15-year-old boy, who had entered into the accelerated phase, with high-dose intravenous gammaglobulin. The treatment was beneficial in the management of accelerated phase of CHS.