A 17-year-old girl was admitted to our department with a hemorrhagic syndrome due to a serious coagulopathy; prothrombin time (PT) INR was 2.46 and the activated partial thromboplastin time (aPTT) ratio 3.46. Coagulation tests with pooled normal fresh plasma did not correct aPTT because of a coagulation inhibitor, and only partially corrected PT. Factor II activity reached only 5%. Diluted Russell viper venom tests (dRVVT) and kaolin clotting time (KCT) of patient plasma (PP) and of a mixture of PP/normal plasma (NP) detected the lupus anticoagulant (LA). The level of factor II antigen was 10%. We diagnosed systemic lupus erythematosus (SLE) with a rare acquired hypoprothrombinemia-LA syndrome (HLAS). The patient was treated with corticosteroids and high-dose Ig and a normal PT value was re-established.