Purpose: Correlation of body mass index (BMI) with clinical outcome in patients with glioblastoma is not well documented. Hence, we studied the association between survival and pretreatment BMI in glioblastoma patients. Methods and Materials: In this retrospective study, only patients with histopathology-confirmed glioblastoma were included. Their BMIs were calculated from height and weight measurements and recorded in medical records at their first examination. Treatment plans for all patients consisted of concurrent radiation therapy and temozolomide, followed by maintenance therapy with temozolomide. The primary endpoint was overall survival (OS). Univariate and multivariate Cox proportional hazards models were used to estimate the mortality risk associated with BMI as a continuous and categorical variable. A BMI of 18.5 to 24.9 kg/m 2 was classified as normal, 25.0 to 29.9 kg/m 2 as overweight, and ≥30.0 kg/m 2 as obese. Results: Data from 392 patients treated from January 2008 through June 2016 were analyzed. At a median follow-up of 48.6 months, the median OS was 13.5 months in normal subjects, 15.4 months in overweight subjects, and 15.1 months in obese subjects. A total of 81% of the patients died. The hazard ratios for overweight and obese patients were 0.70 (95% confidence interval, 0.54-0.92; P =.009) and 0.66 (95% confidence interval, 0.45-0.98; P =.04), respectively, when adjusted for age, Karnofsky performance score, and extent of resection. Sex, diabetes, and hypertension had no significant interactions. Conclusions: Patients with elevated BMIs had significantly better OS in our series of patients. The mechanism of this interaction needs to be explored further to understand this association. © 2018 Elsevier Inc.