We describe a 41-year-old woman, in whom antiphospholipid antibody syndrome (APS) occurred at presentation, before the detection of an ovarian endometrial adenocarcinoma. This syndrome was characterized by widespread and worsening thromboembolism and it did not respond to conventional anticoagulant treatment. The paraneoplastic nature of this APS was strongly suggested by the disappearance of both thromboembolism and antiphospholipid antibodies only after surgical removal of the cancer.