Acquired haemophilia A is a rare disorder caused by spontaneous formation of auto-antibodies (inhibitors) against coagulation factor VIII. This can lead tolife-threatening haemorrhages. Six to twenty-two percent of patients with acquired haemophilia have an underlying malignancy. We describe a 69-year-old woman with metastatic breast cancer and non-small cell lung carcinoma who presented at the emergency room with spontaneous bruising, and who was using a vitamin K antagonist. She had a prolonged activated partial thromboplastin time (aPTT) due to a coagulation factor VIII deficiency caused by factor VIII antibodies. She was treated with prednisone and cyclophosphamide.