Background:Glioblastoma with oligodendroglioma component (GBMO) is a recently classified subtype of glioblastoma, which carries different clinical and prognostic outcomes, being frequently misdiagnosed. Both glioblastoma and GBMO are mainly seen in older ages, such as the 5th and 6th decades of life, being an extremely rare occurrence in children or adolescents and more frequent in male patients. Case report: A 15-year-old girl, presented with history of daily headache, not relieved by painkillers, vomiting, blurred vision and strabismus. Magnetic resonance imaging of the brain revealed expansive tumour on left temporo-occipital lobe. Patient was submitted to intracranial exeresis, along with histopathological examination: glial neoplasm with areas of pleomorphism, hyperchromatism, anaplasia, foci of oligodendroglial component, perinuclear halo and ramified capillaries, resembling oligodendroglioma, necrosis and intense mitotic activity. The immunohistochemical analysis revealed positive Glial Fibrillary Acidic Protein (GFAP), synaptophysin, Ki-67 (MindBomb E3 ubiquitin protein ligase 1 – MIB-1)and hyperexpression of Epidermal Growth Factor Receptor (EGFR), indicating GBMO. Subsequently, Fluorescence in situ Hybridization (FISH) showed 1p/19q codeletion and Isocitrate Dehydrogenase 1 (IDH 1) mutation, suggesting an oligodendroglioma component. Tumour resection was total and symptoms disappeared. Afterwards, she started adjuvant oral chemotherapy with temozolomide. Treatment was completed nine months after the diagnosis, with no greater symptoms or complications and complete remission. Conclusion: GBMO must be considered as a possible diagnosis when confronted with a malignant glioma with oligodendroglial tumour component, independent of age or genre. Necrosis upon histopathological examination has a strong relation to shorter median overall survival. IDH mutation and 1p/19q codeletion should be analyzed by immunohistochemistry. Total tumour resection, with adjuvant treatment (chemotherapy with temozolomide and radiotherapy), increases benefits and improves prognosis.