Ferumoxytol iron nanoparticles are used as an off label molecular MR imaging contrast agent in patients with reduced renal function precluding gadolinium administration. Glioblastoma molecular features are now recognized as an integral component of glioma pathogenetic classification and clinical outcome. IDH1 mutation accounts for approximately 10% of glioblastoma. The absence of a reliable noninvasive biomarker of glioblastoma IDH mutation prompted this retrospective study to determine if Ferumoxytol MR Imaging is diagnostic of IDH mutational status. We observed that the presence of increased Ferumoxytol to Gadolinum enhancing ratio was a significant 3T MR imaging biomarker for IDH mutational status in recurrent glioblastoma and the differentiation of pseudoprogression.