Fatal intracranial hemorrhage was the first and only manifestation of hemophilia B in a 6-week-old boy. A maternal great uncle had mild bleeding difficulties, but the maternal grandfather had a negative history with a factor IX level of 16%. The true incidence of significant central nervous system (CNS) bleeding in infant hemophiliacs is unknown, but reported cases suggest that intracranial hemorrhage may be more common in hemophilia B than in hemophilia A. Lumbar puncture is not contraindicated in hemophilia and should be done in the presence of CNS signs not only to establish the diagnosis of hemorrhage, which is treatable, but also to rule out infection, which may increase the tendency to bleed. The diagnosis of hemophilia should be considered in any baby who presents with signs suggesting intracranial hemorrhage.