In this study, the developmental proliferation of human brain vessels, from the fetal to the adult stage, was analyzed by immunohistochemical methods using antitype IV collagen, antilaminin, and antifibronectin antibodies. Examination of the frontal lobe indicates that these antibodies bind to the vessels, both arteries and veins. During cortical angiogenesis, the density and diameter of vessels increase rapidly from about 26 weeks gestation and peak at 35 weeks; after 35 weeks, the density and diameter of vessels are the same as those in adult brain. The white matter demonstrates no major changes in vessel density, although the pattern of the changes in vessel diameter resembles that of the cortex. Small immunopositive spots suggesting neovascularization reveal the same developmental tendency as the density of vessels in the cortex and white matter; therefore, it appears that neovascularization in the fetal brain during development is more rapid than cortical expansion and is equal to the growth of white matter. Neovascularization may be closely related to normal brain development and may play an undefined role in perinatal cerebrovascular insults.