Diffuse astrocytoma (DA), anaplastic astrocytoma (AA), and glioblastoma (GBM) are defined by the World Health Organization (WHO) based on IDH-mutational status. The vast majority of IDH-mutated gliomas (90% of which involve a mutation in IDH1 R132H, which can be assessed by IDH1 immunohistochemistry [IHC]) occur in persons younger than 55 years of age. This raises the question as to the prevalence of IDH-mutant tumors in older persons and whether the gliomas in older patients should be routinely tested. Since January 1, 2014, we have employed a standard screening panel for all gliomas regardless of patient age. From 578 total gliomas tested, 88 were IDH-mutant DA/AA/GBMs and 11 IDH-mutant tumors were in persons age 55 and older. Of the 11 IDH-mutant examples in the older group, 9 were first clinical presentations of the tumor, 4 of which were in persons age 70 or older (oldest, 76 years). We assessed whether the typical profile of nuclear ATRX loss with or without strong nuclear p53 IHC occurred in these and younger patients and found that ATRX/p53 IHC patterns paralleled those in younger patients. We conclude that, although infrequent, IDH IHC is strongly recommended for all ages of adult patients with diffuse gliomas.