A 45 year-old Asian female presented with new onset of progressive ataxia and underwent resection of a pontocerebellar meningioma. A catastrophic intracranial hemorrhage complicated recovery. Her preoperative coagulation tests were within reference limits. Detailed analysis revealed a very low factor XII level concomitant with prolonged aPTT, but no other coagulation abnormalities were detected. In the discussion, the role of factor XII is described with special emphasize on the novel understanding of the coagulation pathway.