Porcine factor VIII (pFVIII), which is used to control bleeding in patients with congenital or acquired haemophilia who have high-titre neutralizing antibodies to human FVIII, is not known to increase the risk of arterial or venous thrombosis. We have recently encountered a patient with acquired haemophilia who developed a thrombotic left middle cerebral artery distribution stroke while being treated with pFVIII. To our knowledge, this is the first such reported thrombotic event. We speculate that platelet activation induced by pFVIII may have contributed to thrombosis and suggest that pFVIII be used with caution in elderly patients with pre-existing cardiovascular risk factors.