A case of the syndrome of sea‐blue histiocyte is presented in a 53‐year‐old Japanese woman, which is the first recorded case in Japan. The patient had hepatosplenomegaly, bleeding manifestations, mild thrombocytopenia, fatty metamorphosis and cirrhosis of the liver, as well as abnormal serum lipid profiles. Her parents were consanguineous and her maternal grandmother with hepatomegaly died of hepatic failure. Histologically, peculiar histiocytes containing numerous, intracytoplasmic sea‐blue stained granules on May‐Giemsa stain were demonstrated in biopsy materials of the bone marrow, lymph node and liver. The sea‐blue granules in these histiocytes proved to have histochemical staining characteristics of lipogenic ceroid‐like pigment. Ultrastructurally, these granules showed membrane‐bound, pleomorphic inclusions of heterogeneous nature, including electron‐dense amorphous or variegatedly osmiophilic, frequently laminated materials. Enzyme cyto‐chemically, localization of acid phosphatase activity was demonstrated in and around the intracytoplasmic inclusions. With regard to the pathogenesis of the sea‐blue histiocytes in this case, it may be suggested that the existence of the abnormality in lipid metabolism plays an imporant role in intralysosomal ceroidogenesis