Introduction The phenotypic heterogeneity of diffuse gliomas is still inconsistently explained by known molecular abnormalities. Here, we report the molecular and radiological features of diffuse grade WHO II and III gliomas involving the insula and its potential impact on prognosis. Methods Clinical, pathological, molecular and neuro-radiological features of 43 consecutive patients who underwent a surgical resection between 2006 and 2013 for a grade II and III gliomas involving the insula was retrospectively analyzed. Results Median age was 44.4 years. Eight patients had oligodendrogliomas, IDH mutant (IDH mut ) and 1p/19q-codeleted (6 grade II, 2 grade III). Twenty-eight patients had diffuse astrocytomas, IDH mut (22 grade II and 6 grade III) and seven patients had grade II diffuse astrocytomas, IDH wt (A-IDH wt ). Vimentin staining was exclusively recorded in tumor cells from A-IDH wt (p = 0.001). Mean cerebral blood volume (CBV) (p = 0.018), maximal value of CBV (p = 0.017) and ratio of the corrected CBV (p = 0.022) were lower for A-IDH wt . Volumetric segmentation of ADC allowed the identification of the tumor cores, which were smaller in A-IDH wt (p andlt; 0.001). The tumor occurrences of A-IDH wt were exclusively located into the temporo-insular region. Median progression-free survival (PFS) and overall survival (OS) were 50.9 months (95% CI 26.7–75.0) and 80.9 months (60.1–101.6). By multivariate analysis, A-IDH wt (p = 0.009; p = 0.019), 7p gain and 10q loss (p = 0.009; p = 0.016) and vimentin positive staining (p = 0.011; p = 0.029) were associated with poor PFS and OS respectively. Conclusions Insular low-grade A-IDH wt presented with poor prognosis despite a smaller tumor core and no evidence of increased perfusion on MR imaging. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.