We report the case of a 71-year-old man on warfarin for chronic atrial fibrillation presenting with a massive spontaneous soft tissue bleed. Despite reversing the effects of warfarin with large doses of intravenous vitamin K and fresh frozen plasma, bleeding continued, and his prothrombin time and activated partial thromboplastin time remained prolonged. The prothrombin time and activated partial thromboplastin time failed to correct with 50% normal plasma. Further investigations confirmed a lupus inhibitor with low levels of factors II, V, VII and XI. Factor II, V and XI levels normalized, however, when the patient's plasma was diluted 1:16 in buffer, suggesting the lupus inhibitor may have been interfering with these factor assays causing artefactual low results. Factor VII levels remained consistently low at all dilutions. The patient subsequently died following a massive left haemothorax despite surgical intervention and treatment with activated recombinant factor VII concentrate. We presumed the primary problem was bleeding from a local vascular lesion but the patient was never well enough to undergo confirmatory angiography. This case highlights the fact that patients with lupus inhibitors can develop severe haemorrhagic complications, and illustrates the complexities involved in both the investigation and treatment of abnormal bleeding in these patients.