© The Author(s) 2015. Background. Complementary therapy (CAM) is common in cancer patients. We undertook this study to assess the association of complementary therapy usage with mortality in glioblastoma (GBM) patients. Methods. The analysis was based on 470 patients. Information on current use of CAM was collected in structured interviews conducted a median of 6 weeks following GBM diagnosis. Proportional hazards regression was used to estimate hazard ratios (HRs) for GBMrelated death according to the use of individual supplements with multivariate adjustment for known prognostic factors including age, KPS, and extent of tumor resection (ESR). Results. Use of CAM agents was common, with 77% of the cohort reporting CAM usage. No mortality association was observed with the use of multivitamins (HR = 0.91; P = .40) or omega-3 fatty acids (HR = 1.07; P = .69). Patients taking vitamin D as an individual supplement (containing higher dosages than in a multivitamin) had reduced mortality when compared with nonusers (age-adjusted HR = 0.68; P = .02). However, the association was diminished after adjustment for KPS and ESR (HR = 0.74; P = .09). Use of herbal supplements was also associated with reduced mortality (HR = 0.58; P = .04). Vitamin E users had a nonsignificantly higher mortality when compared with nonusers (HR = 1.54; P = .09). Conclusions. Use of CAM is common in GBM patients. These exploratory analyses suggest no mortality association with the use of multivitamins or omega-3 fatty acids. Associations observed with vitamins D and E merit further investigation.