Venous thromboembolism (VTE) is a common problem among patients with glioblastoma multiforme (GBM) and with some other cancers. Here, we evaluated genetic and non-genetic potential risk factors for VTE among GBM patients. A cohort of 139 patients treated with concomitant radiotherapy and temozolomide were included in the study. Next generation sequencing and genotyping approaches were applied to assess genetic risk factors in the haemostatic system. Clinical data including surgery, reoperation as well as blood group and patient information such as age and gender were available from patient records. Logistic regression analysis was performed to asses VTE risk. In the study 47 patients (34%) were diagnosed for VTE during the course of their disease. When genetic and non-genetic potential risk factors were evaluated, only B blood group was found to be significantly associated with VTE incidence (odds ratio OR = 6.91; confidence interval CI = 2.19–24.14; P = 0.001). In contrast, A and O blood groups did not correlate with VTE risk. Frontal lobe tumor location also seemed to slightly increase VTE risk compared to other brain sites (OR = 3.14; CI = 1.1–10.7) although the significance level was at borderline (P = 0.05). Current study identified B blood group as the component in non-O blood groups that is responsible for increased VTE risk. In conclusion, these results suggest for the first time that B blood group is predictive for VTE incidence among patients with glioblastoma, information that may be potentially valuable when selecting GBM patients who are at risk for VTE for anticoagulant prophylaxis. •Thrombosis is a major problem in patients with high grade glioblastoma tumors (GBM).•We investigated several potential thrombosis risk factors in 139 GBM patients.•B blood group but not A or O blood groups significantly increased thrombosis risk.•GBM patients with B blood group could benefit from thrombosis prophylaxis.