Although uncommon, acquired hemophilia A (HA) is associated with a high rate of mortality due to severe bleeding. In spite of many hypotheses regarding the cause of acquired HA, there is as yet no established theory. In this study, we investigated the possibility that mutation(s) in the F8 gene may be correlated with the development of inhibitory autoantibodies. Direct sequencing analysis was performed on all 26 exons of the F8 gene of 2 patients exhibiting acquired HA. Both patients were found to share a common point mutation (c.8899G>A) in the 3'-untranslated region (3'-UTR) of exon 26. This is the first report on the genotyping of F8 in the context of acquired HA.