A 71 year-old man with adult onset Still's disease was admitted to our hospital because of fever, sore throat, myalgia and macular nonpruritic salmon pink eruption. He was treated with prednisolone, 40 mg daily and these symptoms disappeared. When the dose of prednisolone was reduced to 30 mg daily, he began to notice fever. 5 days later he developed adult respiratory distress syndrome (ARDS). The dose of prednisolone was increased to 50 mg daily and oxygen administration was started. All symptoms began to improve immediately and the dose of prednisolone was decreased to 40 mg daily. 10 days later he noticed fever and skin rash. Laboratory investigation showed platelet counts of 69,000/mm3, a ferritin of 37,000 ng/ml, and increased fibrinogen degradation product, indicating increased activity of adult onset Still's disease associated with disseminated intravascular coagulation (DIC). The dose of prednisolone was again increased to 60 mg daily, and 100 mg of nafamostat mesilate was administrated intravenously. All above symptoms associated with adult onset Still's disease and DIC disappeared. The dose of prednisolone was gradually decreased and the clinical course was uneventful with daily administration of 10 mg of prednisolone. Although there are a couple of case report which described the association of adult onset Still's disease with either ARDS or DIC, the association of adult onset Still's disease with both ARDS and DIC have not been reported yet.