A 71-year-old man was diagnosed as having an abdominal aortic aneurysm when he was treated for idiopathic interstitial pneumonia (IIP). Three years later, he developed severe thrombocytopenia and had disseminated intravascular coagulation (DIC) that was associated with the inflammatory abdominal aortic aneurysm (IAAA). The coagulation abnormalities were corrected by low-molecular weight heparin, however the platelet count remained low. Bone marrow showed normocellularity with an increase of immature and mature forms of megakaryocytes. Platelet-associated IgG level was high. These findings suggested that the patient had severe thrombocytopenia caused by unusual complications of immune thrombocytopenic purpura and IAAA-associated DIC.