Diagnosis criteria, pathogenic mechanisms, incidence and prevalence of the Antiphospholipid Syndrome are focused in a brief review. Hypoprothrombinemia (HPT) may be hereditary or acquired; the first is rare and with recessive autossomic transmission. We report the case of a 66-year-old white woman with Systemic Lupus Erythematosus (SLE), autoimmune haemolytic anaemia, periostitis, haematomas, bleeding leg ulcer and rectal haemorrhages; she had decreased levels of the prothrombin. Haemorrhagic episodes were related with the anti-prothrombin specificity of Lupus Anticoagulant (LA) detected. The SLE/LA/HPT association is less frequent than the correlated to SLE/LA/anti- ß2Glycoprotein I antibodies and was first reported in 1960 by Rapaport et al, in an 11-year- -old girl with severe haemorrhagic manifestations.