Introduction: H3.3 G34R/V mutation is predominantly identified in the supratentorial nonmidline tumors. However, this tumor is not yet categorized as an entity in 2016 WHO CNS classification. More information is necessary to further determine the characteristics of this tumor. Case Presentation: Three cases of adolescent hemispheric glioma were treated in our institution. All tumors showed the characteristics of huge tumor size with mild peritumoral edema on T2WI/FLAIR, hyperintense on DWI, and slight partial enhancement by gadolinium. The single-voxel proton MR spectroscopy revealed characteristics of high choline peak, marked decrease in N-acetyl aspartate peak, and small lactate peak. The histopathological diagnosis, based on 2007 WHO CNS classification, was high-grade glioma in 2 cases and a PNET. Immuno­staining revealed that the tumor cells were positive against H3.3 G34R, H3K27me3, and p53 antibodies and negative against H3K27M, IDH1-R132H, ATRX, and Olig2 antibodies. Pyrosequencing analysis confirmed H3.3 G34R mutation, IDH-wildtype, and BRAF-wildtype. Conclusion: Radiological and immunostaining findings are characteristic in our 3 cases of H3.3 G34-mutant glioma. It is essential to consider H3.3 G34-mutant glioma as a differential diagnosis particularly in pediatric and adolescents and young adult hemispheric tumors.