Intraoperative MRI (iMRI) has increasingly been used for image-guided resection of glioblastoma. Survival for glioblastoma with current therapy has been poor, averaging 15 months¹. Prior studies have demonstrated increased extent of resection with the use of iMRI in glioblastoma^{2, 3}. Other studies have also demonstrated increased overall survival with increased extent of resection⁴. Few studies to date have examined MRI guided resection as an independent predictor of overall survival for glioblastoma, with published series limited by small sample size or inclusion of lower grade tumors^5-7. We retrospectively analyzed 161 cases of glioblastoma treated at a single institution to determine the effect of resection with iMRI on outcomes in patients with glioblastoma.Approval for the study was obtained from the hospital IRB. We performed a chart review to identify 161 subjects with initial resection of glioblastoma at our institution over a seven-year period. We identified 68 subjects who had conventional surgery using pre-operative stereotactic MRI and 93 subjects where additional intraoperative MR imaging was performed during resection. Intraoperative imaging was performed on a 1.5T MRI scanner (IMRIS, Minneapolis, Minnesota, USA) using T1, T2, and gadolinium enhanced T1 weighted sequences. Baseline demographics and outcomes were obtained on all subjects. Statistical comparisons across type of brain surgery by various demographic/characteristics were performed by a chi-square test for categorical data and the general Wilcoxon test for continuous data. Kaplan-Meier curves were used to estimate the probability of survival⁸. The log-rank test was used to complete comparisons. Cox regression was used to look at the independent effect of iMRI on survival. All reported p-values were 2-sided. All analyses were performed using SAS version 9.3 (SAS Institute, Cary, NC).There were no significant demographic differences between the iMRI and conventional surgery groups (Table 1). Recipients of iMRI in our study had a higher probability of gross total resection than did recipients of conventional surgery (63% [95% CI, 54-73%]) vs 41% [95% CI, 29-53%]; p < 0.01). When restricted to a follow-up of 6 months after the procedure (Table 2), overall survival (OS) among the iMRI group showed a statistically significant benefit as well (89% [95% CI, 81-94%] versus 78% [95% CI, 66-86%]; p=0.04). However, after extending the follow-up (Figure 1), there did not appear to be a difference in median time to OS between iMRI and conventional therapy (17 months vs 15 respectively, p=0.59). OS was longer for younger age groups, p=0.03 (Table 3), as has been reported in prior studies ⁹.Our research confirmed the advantage to iMRI in achieving a greater number of gross total resections. We found that there is a short-term OS advantage to iMRI at 6 months. No statistically significant survival benefit was noticed at long term follow-up. These findings may be due to the heterogeneous genetic makeup of glioblastoma ¹⁰. A subgroup of subjects may gain a short-term advantage from greater extent of resection. Long term survival may be determined by genetic susceptibility to chemotherapy and radiotherapy, and therefore extent of resection may be less influential in the long term. Analysis of genetic mutations is not available for our study group. Future studies including survival analysis with subgroups analyzed for specific chromosome or gene mutations may provide more information. Use of iMRI for initial resection of glioblastoma provides greater extent of resection as well as a short-term survival benefit. Conventional surgery and iMRI groups demonstrated equivalent survival between 12-36 months. Limitations of the study include retrospective data collection and lack of availability of information on molecular profiles of the tumors as well as functional status of patients. Additional prospective studies are warranted to better appreciate the overall effect of iMRI in patients with glioblastoma.