Background: The development of predictive and prognostic biomarkers in malignant gliomas is the subject of intense research designed to provide personalized therapies for patients with these cancers. The availability, ordering, and clinical influence of molecular tests are not well described. This study was conducted to assess the current use of available biomarkers in patients with glioblastoma (GBM). Methods: A questionnaire consisting of 13 multiple-choice and 2 open questions was distributed online to members of the neuro-oncology community in the United States using email addresses published in the 2010 meeting program of the Society for Neuro-Oncology. All answers were collected between January 5 and 16, 2011. Results: The response rate to this survey was 30.4% (320/1053). Participants who did not see GBM patients were excluded from analysis (n=73). The 247 qualified respondents saw 0-2 (22%), 3-10 (34%), 11-30 (30%), or >30 (15%) patients with GBM per month. When seeing patients with newly diagnosed GBM, participants (n=201) reported routinely ordering no molecular tests (33%), MGMT promoter methylation (46%), EGFR amplification (28%), 1p19q co-deletion (27%), EGFR expression (26%), p53 mutation (24%), PTEN mutation or deletion (21%), IDH1/IDH2 mutation (15%), EGFRvIII mutation (15%), PDGFR expression (6%), or PIK3CA mutation (1%). The following percentages of clinicians seeing >3 patients with GBM/month noted that molecular tests “always” or “almost all the time” influenced their management of patients with GBM: 1p/19q co-deletion 20% (28/142), MGMT promoter methylation 11% (17/158), EGFR expression 3% (4/134), EGFR amplification 3% (4/143), EGFRvIII mutation 3% (4/139), IDH1/IDH2 mutation 2% (3/132), p53 mutation 1% (1/133), PDGFR expression 0% (0/131), PIK3CA mutation 0% (0/126), or PTEN mutation or deletion 0% (0/133). Conclusions: An estimated two thirds of clinicians routinely order one or more molecular biomarkers for patients with newly diagnosed GBM. The most commonly ordered tests were MGMT promoter methylation, EGFR amplification, and 1p19q testing. However, the impact of the molecular test results on clinical decision making remains modest.