Acquired factor VIII inhibitor was found in a 69-year-old white male with insulin-dependent diabetes mellitus. He presented with left lower abdominal pain and hematoma after a fall. Preoperative hemostasis studies were normal except for prolonged aPTT. Prolonged aPTT was not corrected by 1:1 mixture with normal fresh plasma and incubation showed further prolongation with time. Factor VIII:c was 3.5%. The inhibitor titer was 7.5 Bethesda units. The possible mechanism causing antibody to factor VIII was postulated to be an autoimmune process and/or increased immunogenicity owing to glycosylation of factor VIII coagulant protein.