We demonstrated the developmental characteristics of vessel density in the human brain, using an antibody against CD31, which specifically reacts with endothelium. In the cerebral cortex and subcortical white matter, the vessel density was low at 16-28 weeks of gestation (GW), and then increased after 36 GW. In the deep white matter, the vessel density was high in the middle fetal period (16-24 GW), and then transiently decreased at 28-36 GW, and increasing after 39 GW. In the putamen, the vessel density was high at 20-21 GW, remained high throughout the fetal period, and then rapidly increased after birth. In the basis pontis, the number of vessels increased after 28 GW, and after 32 GW was greater than in the pontine tegmentum. These alterations in vessel density may correlate with the pathogenesis of perinatal brain injury. Thus, the transient decrease of vessel density in the deep white matter may predispose to periventricular leukomalacia in cerebral hypoperfusion. Similarly, the well-developed vascularity in the basis pontis may predispose its relatively immature neurons to neuron necrosis produced by free radical injury.