High-grade gliomas are highly vascularized tumors. Neo-angiogenesis plays a key role in tumor growth and resistance to therapy. A cerebrospinal fluid (CSF) sample could be a useful way to obtain pro-angiogenic predictive or prognostic markers at different stages of the disease. As a first step we looked for pro-angiogenic activity in the CSF of patients with high-grade gliomas. We performed the chicken embryo chorio-allantoic membrane (CAM) assay to study the angiogenic potential of the cerebrospinal fluid (CSF), obtained either by lumbar puncture (LP) or craniotomy from six patients with high-grade brain tumors (three glioblastoma (WHO grade IV), one anaplastic oligodendroglioma (WHO grade III), two anaplastic ganglioglioma (WHO grade III)), and four healthy controls. Significantly increased neo-angiogenesis was observed on the surface of the growing CAM in the 6 patients with high-grade gliomas compared to controls (3.69 ± 1.23 versus 2.16 ± 0.97 capillaries per area (mean ± SD), p<0.005). There was no statistical difference related to the hystological grade of the tumor (WHO grade III or IV), previous treatment (radio-chemotherapy plus temozolomide, temozolomide alone or no treatment), or the site of CSF sample (surgery or lumbar puncture). Our results suggest a pro-angiogenic potential in the CSF of patients with high-grade gliomas.