Immune cells are known to infiltrate human gliomas, but their implication in immunosurveillance is controversial. Since these infiltrates have been observed only at terminal stages of glioma development, it is not defined whether immunoediting occurs in these tumors. Alternatively, defective afferent immunity may delay a potent anti-tumor response, which is then overwhelmed by the tumor outgrowth. Finally, immune cells infiltrating gliomas may have poor anti-tumor competency, or may even promote tumor growth from early stages. In this study, a transgenic mouse model of spontaneous astrocytoma (GFAP-V12HA-ras or RasB8 mice) was analyzed to address these issues. Brain-infiltrating immune cells were characterized at different stages of tumor development. In addition, this model was used to determine whether the local immune balance in spontaneous gliomas could be tilted towards effector immune responses.