We report that Tm4sf1-null embryos are avascular and experience lethality at E9.5, while Tm4sf1-heterozygous embryos are smaller in body size during early embryonic development, and about half die in utero due to an intracranial hemorrhage, which becomes apparent in the intraventricular and subarachnoid space by E17.5. This evidence concerns the gene TM4SF1 and intracranial hemorrhage.