We report the case of an 86-year-old female with an unremarkable past history who suddenly developed severe and generalized bleeding. Laboratory work-up revealed prolonged aPTT, a factor VIII level of 7% and the presence of a factor VIII inhibitor. In spite of whole blood, factor VIII concentrates and immunoglobulin administration, the patient died of multiple hemorrhages on the third day after admission. At autopsy no causal or associated pathology could be found. Chromatographic separation of plasma immunoglobulins showed that the anti-factor VIII activity was associated with the patient's IgG. This inhibition was partially corrected in vitro by injectable immunoglobulin preparation. The case report stresses the discrepancy between the measured levels of inhibitor and the severity of the bleeding; our in vitro results may shed light on the mode of action of intravenous immunoglobulins.