A 50-year-old woman was emergently admitted because of rapidly progressive unconsciousness, renal failure, hepatic dysfunction, hemolytic anemia, thrombocytopenia, and high-grade fever in July, 2008. Based on clinical and laboratory findings, we made a tentative diagnosis of thrombotic thrombocytopenic purpura (TTP) and immediately initiated the plasma exchange (PE). Despite the PE, she developed panperitonitis due to multiple intestinal perforation and massive splenic infarction within a week after the admission. Thrombosis of arterioles at perforated portion in the resected small and large intestines was histologically confirmed. Therefore, we made a definite diagnosis of catastrophic antiphospholipid syndrome (CAPS) based on the presence of antiphosphatidylserine-prothrombin complex antibodies (aPS/PT) throughout the course and lupus anticoagulant that was revealed positive on one occasion, and multiple thrombotic lesions. The underlying disease of CAPS appeared to be lupus erythematosus because of her clinical history and laboratory findings such as persistent leukopenia. Although it has been reported that CAPS causes systemic thrombosis at microvessels mostly within a week from the onset and the mortality rate in this disorder is as high as 50%, we successfully treated her in combination with high-dose corticosteroid, anticoagulation, concentrated human IgG, surgical procedures, and hemodialysis in addition to PE. Early diagnosis of CAPS and immediate start of PE may have contributed to the successful treatment.