Through analysis of transcriptome expression status of ICOS among 1,323 glioma patients, we found that higher ICOS expression correlated with higher malignancy of gliomas, based on the fact that ICOS upregulation was remarkably paralleled with much more aggressive characteristics of gliomas, including glioblastoma, IDH wild type, and mesenchymal subtype, and could serve as an independent prognosticator for worse survival. Here, ICOS is linked to glioma.