We herein present a case of acquired hemophilia A with a normal activated partial thromboplastin (aPTT), intramuscular hematoma and cerebral hemorrhage occurring in a 73-year-old man. The patient visited our emergency department with gait disturbance, pain and swelling in his right leg. Computed tomography (CT) and magnetic resonance imaging (MRI) revealed intramuscular hematoma and intracranial hemorrhage. The results of initial coagulation studies were normal, but repeated coagulation studies revealed an isolated prolongation of the aPTT. Additional laboratory tests confirmed the diagnosis of acquired hemophilia A. If the initial aPTT is normal, we should therefore repeat the aPTT and also perform other coagulation studies including a mixing study, factor VIII level and inhibitor, to investigate the underlying diseases in elderly patients with spontaneous hemorrhaging of unknown etiology.