Aim:Glioblastoma is the most prevalent, fatal malignant cerebral tumor. It is dichotomized as primary and secondary. These two groups differ in terms of clinical course and survival, and this difference is based on the presence or absence of isocitrate dehydrogenase (IDH) mutation. Detection of IDH mutation is important because it has an impact on patient survival, as well as has a therapeutic approach. In the current study, we assessed the presence of IDH1 mutation in glioblastomas using real-time polymerase chain reaction (RT-PCR), which is the gold standard in the diagnosis of IDH1 mutation; by immunohistochemistry (IHC), which is available in most of the pathology laboratories; and by preoperative magnetic resonance imaging, which is a non-invasive method. We also investigated the relationship between these methods and their usability in routine practice.Material and Methods:RT-PCR was performed to evaluate the presence of IDH1-R132H mutation on the blocks of 70 patients diagnosed with glioblastoma, and IDH1 stain was applied to the same blocks as IHC. Radiologically, preoperative magnetic resonance images of the patients were reviewed in terms of tumor size, localization, and presence of non-contrast-enhancing solid tumor component.Results:Evaluation by RT-PCR revealed that 15 (21.4%) patients were IDH-mutant, whereas IHC examination revealed 13 (18.6%) and radiological evaluation revealed 11 (15.7%) patients were IDH-mutant. There was a statistically significant difference between the IDH1 mutation detected by RT-PCR and by IHC or radiological methods (p = 0.034 and p = 0.000, respectively). The sensitivity and specificity of IHC method in detecting IDH1 mutation were 86.6% and 100%, respectively, whereas those of radiological methods were 33.3% and 89%, respectively. Conclusion:Conclusively, radiological and IHC methods can be used in cases where RT-PCR cannot be applied for detecting IDH1 mutation. However, the results need to be confirmed by RT-PCR when necessary as these methods may sometimes overlook some IDH-mutant patients.