The treatment of supratentorial malignant gliomas has continued to be a major problem for neurosurgeons and oncologists. Post-operative conventional radiotherapy is known to prolong survival and to enhance the quality of life. Local persistence of tumor kills the majority of patients. Fast neutron irradiation is being utilized to treat malignant gliomas based on its reputed radiobiological advantages for treatment of large tumors and the encouraging preliminary reports showing tumor eradication in post-radiation biopsy and autopsy specimens. This paper reviews the results of fast neutron irradiation alone and in combination with photons and hypoxic cell sensitizers. Survival comparisons do not show any superiority for neutrons compared to conventional radiation. However, post-neutron radiation tissue samples have shown less aggressive and minimal residual tumor in many instances. At the same time radiation necrosis has emerged as a significant problem. In summary, even though neutron irradiation can eradicate malignant gliomas a therapeutic window has yet to be identified.