Glioblastoma multiforme (GBM) is the most lethal type of brain tumor. The formation of abnormal, dysfunctional tumor vasculature and glioblastoma stem-like cells (GSCs) are believed to be the major components of the inability to treat these tumors effectively. We analyzed 70 glioblastoma samples by immunohistochemistry and double immunofluorescence staining. The immunohistochemical expression of the putative brain tumor stem cell markers CD133 and Nestin in paraffin sections was analyzed using morphometry. In all GBM samples, CD133 or Nestin was expressed in tumor and endothelial cells. Double immunofluorescence stainings showed that the two different marked GSCs were found accumulated around the CD31+ blood vessels and CD133/CD31 or Nestin/CD31 co-expression was found in the endothelial cells and GSCs. Furthermore, the vascular endothelial growth factor (VEGF) and the endothelial marker CD31 were co-expressed in GSCs. Therefore, GSCs not only showed distinct perivascular distribution but were capable of differentiating into endothelial cells. We demonstrate that GSCs contribute directly to the tumor vasculature by endothelial cell differentiation. GSCs and tumor vascularization are closely related to each other, not only in the regional distribution but also in biological function. These findings describe a new mechanism for tumor vasculo-genesis and may provide new insights for targeted therapy against brain tumors.