Acquired haemophilia is a potentially life-threatening bleeding disorder. Its early diagnosis and treatment is of major importance. We evaluated the elapsed time between the first presentation of the bleeding symptoms and the correct diagnosis in the cases of the acquired haemophilia patients referred to our centre between 1999 and 2011. The causes and consequences of the often delayed diagnosis were also examined. The clinical and laboratory data of 13 patients with acquired haemophilia were analysed. Eleven patients had inhibitors to factor VIII (FVIII), in one case the autoantibody developed to factor XIII (FXIII) and in one to factor V (FV). The median period between the onset of the bleeding symptoms and the correct diagnosis was 1.5 months (3.0 days-9.0 months). In four cases 4.0-9.0 months were needed to establish the diagnosis. The main reason of this delay was that either the prothrombin time was used exclusively to evaluate haemostasis in primary care and also in some secondary care centres, or the prolonged activated partial thromboplastin time went unnoticed despite the obvious bleeding symptoms. Our observation underlines the importance of early referral of patients with unexplained bleeding symptoms to centres with appropriate laboratory facilities and experience in the diagnosis of bleeding disorders.