Bleeding symptoms of acquired FXI deficiency are poorly related to residual FXI activity [1] and include mild or absent bleeding [4, 6, 7], mucocutaneous bleeding [8], postsurgical hemorrhage [5, 10], and life-threatening [11] or fatal intracranial bleeding, as here reported. Here, F11 is linked to hyperinsulinemic hypoglycemia, familial, 4.