This retrospective study profiled subjects with glioblastoma multiforme (GBM) who had previously received therapeutic radiation. A chart review was conducted of 100 adult patients diagnosed with GBM and referred to a major medical center in the southwestern United States. Seventeen patients received previous radiation therapy with an average dose of 48.5 Grey (Gy) and an average latency period of 15 years between initial therapy and GBM diagnosis. Of these 17, four white females fit all four attribution criteria for radiation-induced GBM. Two had been treated with radiation for prolactinomas, one for pinealoma and one for squamous cell cancer of the ethmoid sinus. The addition of these four case studies to the previously published descriptions of 80 cases of gliomas, 36 of which were GBM, subsequent to radiation therapy provides additional support for considering therapeutic radiation as a risk factor for GBM development.