A 59-year-old man with pernicious anemia (vitamin B12 deficiency) was admitted because of rapidly developing pancytopenia with the symptoms of influenza. Laboratory data indicated that the pancytopenia was manifested by influenza virus-associated hemophagocytic syndrome. In the patients with pernicious anemia, it is known that there are immunologic disturbances in either humoral and cellular immunity and increased hematopoiesis due to ineffective hematopoiesis. This patient was thought to have developed influenza virus-associated hemophagocytic syndrome due to the immunologic and hematopoietic abnormality in the pernicious anemia.