Acquired hemophilia is caused by antibodies against coagulation factors, especially against factor VIII. As it is a low prevalence disease, our objective is to present an idiopathic case of acquired hemophilia to facilitate decision-making in clinical practice for others, exposing the therapeutic modality used. 65 years old woman, started with non-trauma hematomas, with asthenia, adynamia and dyspnea. Laboratory studies showed anemia (hemoglobin 7.1 g/dl, hematocrit 21%, mean corpuscular volume 91 fl, mean corpuscular hemoglobin 29.6 pg) and long clotting times (activated partial thromboplastin time 100 seconds) and with prothrombin time and International Normalized Index (17 seconds and 1.2 seconds respectively). So, plasma dilution tests were performed with plasma, without aPTT correction (1:2, 76.6 seconds; 1: 4, 60 seconds; 1: 8, 45 seconds) evidencing the presence of the inhibitor. The diagnosis was confirmed by the decrease in factor VIII (1%) and the presence of the factor VIII inhibitor (256 UB). The treatment started with prednisone and cyclophosphamide. Due to the presence of severe bleeding, treatment with activated prothrombin complex concentrate (CCpa) was required. Subsequently, Rituximab was prescribed, with clinical improvement and increased levels of hgb and reduced aPTT from the first week of treatment. The approach of acquired hemophilia should include control of the bleeding, the search for the etiology ruling out of the main causes of malignant neoplasms according to age and gender, and the immediate initiation of immunosuppression to decrease inhibitor levels.