A 66-year-old man was admitted to our hospital for fever on January 19, 1998. He began showing periodic high fever in June 1997 and an increased serum LDH in August 1997. His history included surgery for esophageal cancer in 1993. On admission, the patient's body temperature was 38.5 degrees C. Physical examination was negative for lymphadenopathy, hepatosplenomegaly, and skin rash. Peripheral blood revealed a hemoglobin level of 8.6 g/dl and a platelet count of 7.9 x 10(4)/microliter. Bone marrow examination showed hypocellularity with marked histiocytic hemophagocytosis. The various bacterial cultures were negative. Serum LDH was elevated to 1,606 IU/l, and ferritin was greater than 3,000 ng/ml. Antinuclear antibodies were negative. No significant elevation of viral antibody titers including that to Epstein-Barr virus was found. Hemophagocytic syndrome (HPS) was diagnosed, but no underlying diseases was identified. The patient's condition was complicated by interstitial pneumonia and pleural effusion. gamma-globulin and pulse methylprednisolone both proved ineffective for the HPS; however, complete remission was achieved with cyclic intravenous administration of etoposide (VP-16, 150 mg/day). Interestingly, the interstitial pneumonia resolved promptly with etoposide therapy. The patient relapsed, in July 2001, exhibiting high fever, cytopenia, and marrow hemophagocytosis. His condition was ameliorated by administration of etoposide. This was a rare case of chronic and recurrent HPS of unknown etiology accompanied by interstitial pneumonia. Etoposide should be considered as a primary therapy for HPS and its complications in cases such as our patients.