In April, 1991, a 61-year-old man was admitted to our hospital because of pancytopenia and disseminated intravascular coagulation (DIC). Five years prior to admission he had developed high fever, skin eruption and arthralgia which had been improved by antibiotics, but recurred. Steroid therapy was ineffective for pancytopenia and DIC. Laboratory findings were as follows: RBC count, 274 x 10(4)/microliters; WBC count, 470/microliters; Platelets, 6.4 x 10(4)/microliters; fibrinogen, 153mg/dl; FDP, 67.0 micrograms/ml; FDP-D.Dimer, 13040ng/ml; thrombin-antithrombin complex, > 60.0ng/ml; and plasmin alpha 2-plasmin inhibitor complex, 10.3 micrograms/ml. As we suspected adult onset Still's disease on the basis of clinical course, we treated him with methylprednisolone pulse therapy, which was, however, ineffective. leukocytopenia, thrombocytopenia and DIC improved after cyclosporine treatment. Since cyclosporine is known to be very effective to autoimmune diseases, we speculate that in this patient immunological mechanism may be involve in the pathogenesis of DIC.