BACKGROUND: Patients with malignant gliomas present with variation in neurocognitive function (NCF) not attributable to lesion size or location alone. A potential contributor is the rate at which tumors grow, or "lesion momentum." Isocitrate dehydrogenase 1 wild type (IDH1-WT) are more proliferative and aggressive than IDH1-mutant (IDH1-M) tumors. We hypothesized that patients with IDH1-WT would exhibit worse NCF than patients with IDH1-M tumors. METHODS: Comprehensive NCF testing was completed in 119 patients with malignant glioma prior to surgical resection. IDH1 status was determined with immunohistochemistry and sequencing. Rates of impairment and mean test performances were compared by IDH1. RESULTS: NCF impairment was significantly more frequent in patients with IDH1-WT tumors in memory, processing speed, visuoconstruction, language, executive functioning, and manual dexterity. Mean performances of patients with IDH1-WT were also significantly lower than those with IDH1-M tumors on measures of learning and memory, processing speed, language, executive functioning, and dexterity. Lesion volume was not statistically different between IDH1-WT and IDH1-M tumors. Tumor and lesion volume on T1-weighted and fluid attenuated inversion recovery MRI were significantly associated with most NCF tests in patients with IDH1-WT, but only significantly associated with a single measure in patients with IDH1-M tumors. CONCLUSION: Patients with IDH1-WT show reduced NCF compared with those with IDH1-M malignant gliomas. Lesion volume is inversely associated with NCF for patients with IDH1-WT, but not IDH1-M tumors. These findings are consistent with the hypothesis that patients with IDH1-WT tumors present with more severe NCF impairment due to greater lesion momentum, which may impede compensatory neuroplasticity and cerebral reorganization.