The impact of isocitrate dehydrogenase (IDH1/2) mutations on the malignant progression of gliomas was investigated by comparing the histopathological features of 53 grade II and III gliomas after recurrence according to the IDH1/2 status. We identified IDH1/2 mutations in 44.4 % (16 of 36) of astrocytic tumors and 70.6 % (12 of 17) of oligodendroglial tumors. Histopathological malignant progression was observed in 68.8 % (11 in 16) and 55 % (11 in 20) of astrocytic tumors with and without IDH1/2 mutations, respectively. There were 8 secondary glioblastomas (GBM) that had progressed from 5 diffuse astrocytomas (DA) and 3 anaplastic astrocytomas (AA) with IDH1/2 mutations. Seven secondary GBMs were derived from 3 DAs and 4 AAs with wild-type IDH1/2. Malignant progression was observed in 47.1 % (8 of 17) of oligodendroglial tumors. All 12 oligodendroglial tumors with IDH1/2 mutations remained as such without progressing to GBM, whereas 3 of the 5 oligodendroglial tumors without IDH1/2 mutations progressed to GBM at recurrence. In conclusion, grade II and III gliomas developed to more malignant histological types, irrespective of the IDH1/2 mutation status, and the monitoring of the IDH1/2 status could be of value to predict the development of GBM in patients with oligodendroglial tumors.