Acquired haemophilia A is rare, autoimmune bleeding disorder caused by the production of autoantibodies against coagulation factor VIII (FVIII). The disorder affects 1.5 people per 1 million population a year, particularly the elderly. Unlike congenital haemophilia, the disease occurs in a similar proportion of men and women. An 86-year-old patient was admitted to the Department of Internal Medicine and Pharmacology with anaemia, progressive weakness, bruising in the subcutaneous tissue, and generaliesd stiffness of joints. Routine blood tests revealed isolated prolongation of activated partial thromboplastin time (aPTT) above 100 s. Activated partial thromboplastin time mixing test also showed prolongation of aPTT equal to 104.2 s. Factor VIII activity was 2%. The patient was referred to the Haematology Department, where a positive titre of anticoagulant 11 (BU) was obtained. After diagnosing acquired haemophilia A, the patient was administered activated prothrombin complex concentrate and prednisone, which resulted in clinical improvement and shortening of aPTT.