Lower-grade gliomas (WHO grade II/III) have been classified into clinically relevant molecular subtypes based on and 1p/19q mutation status. The purpose was to investigate whether T2/FLAIR MRI features could distinguish between lower-grade glioma molecular subtypes. MRI scans from the TCGA/TCIA lower grade glioma database ( = 125) were evaluated by two independent neuroradiologists to assess (i) presence/absence of homogenous signal on T2WI; (ii) presence/absence of "T2-FLAIR mismatch" sign; (iii) sharp or indistinct lesion margins; and (iv) presence/absence of peritumoral edema. Metrics with moderate-substantial agreement underwent consensus review and were correlated with glioma molecular subtypes. Somatic mutation, DNA copy number, DNA methylation, gene expression, and protein array data from the TCGA lower-grade glioma database were analyzed for molecular-radiographic associations. A separate institutional cohort ( = 82) was analyzed to validate the T2-FLAIR mismatch sign. Among TCGA/TCIA cases, interreader agreement was calculated for lesion homogeneity = 0.234 (0.111-0.358), T2-FLAIR mismatch sign = 0.728 (0.538-0.918), lesion margins = 0.292 (0.135-0.449), and peritumoral edema = 0.173 (0.096-0.250). All 15 cases that were positive for the T2-FLAIR mismatch sign were -mutant, 1p/19q non-codeleted tumors ( < 0.0001; PPV = 100%, NPV = 54%). Analysis of the validation cohort demonstrated substantial interreader agreement for the T2-FLAIR mismatch sign = 0.747 (0.536-0.958); all 10 cases positive for the T2-FLAIR mismatch sign were -mutant, 1p/19q non-codeleted tumors ( < 0.00001; PPV = 100%, NPV = 76%). Among lower-grade gliomas, T2-FLAIR mismatch sign represents a highly specific imaging biomarker for the -mutant, 1p/19q non-codeleted molecular subtype. .