Telomerase is a ribonucleoprotein that consists of a RNA component for synthesizing telomeric DNA repeats onto chromosome ends, so that telomere length can be maintained; telomerase activation in general signifies immortalization of cells. Because the telomerase activity of only a few cases of nonastrocytic gliomas and low-grade astrocytic gliomas have been examined before, telomerase activity from a broad spectrum of astrocytic and nonastrocytic gliomas were examined in this study. A total of 119 brain tumor samples, including 16 pilocytic astrocytomas, one dysembryoplastic neuroepithelial tumor (DNT), two pleomorphic xanthoastrocytomas (PXA), 15 ependymomas, 21 oligodendrogliomas, 13 grade II astrocytomas, 13 anaplastic astrocytomas, and 38 glioblastoma multiforme tumors (GBM), were studied, using a polymerase chain reaction (PCR)-based telomeric repeat amplification protocol assay. All pilocytic astrocytomas, DNT, PXA, and myxopapillary ependymomas were telomerase negative. Three of 13 (15.4%) classical ependymomas, 2 of 14 (14.3%) grade II oligodendrogliomas, and three of seven (42.9%) anaplastic oligodendrogliomas had detectable telomerase activity. The frequency of telomerase expression in ependymomas and oligodendrogliomas was lower than those observed in astrocytic tumors: fibrillary astrocytoma, 23.1%; anaplastic astrocytoma, 23.1%; and GBM, 26.3%. The mean age of telomerase-positive GBM patients (61.7 years) was significantly higher than that of telomerase-negative GBM patients (47.8 years, P=.002). These results suggest that telomerase activation may occur early in glial tumorigenesis, and astrocytomas may have mechanisms of immortalization other than telomerase activation.