BACKGROUND: Glioblastomas have a poor prognosis, possibly because of a subpopulation of therapy-resistant stem cells within the heterogeneous glioblastoma. Because the subventricular zone is the main source of neural stem cells, we aimed at characterizing the subventricular zone using diffusion tensor imaging (DTI) to show subventricular zone involvement in glioblastoma. METHODS: We prospectively included 93 patients with primary glioblastomas who underwent preoperative DTI. The nonenhancing high fluid-attenuated inversion recovery (FLAIR) signal was used to describe the infiltrative tumor margin. We used a 5-mm margin surrounding the lateral ventricles to define the subventricular zone. The subventricular zone with high FLAIR was compared with the subventricular zone without high FLAIR, control high FLAIR outside the subventricular zone and control contralateral normal-appearing white matter. Normalized DTI parameters were calculated and compared between the different regions. RESULTS: The subventricular zone with high FLAIR showed increased isotropic p values compared with the subventricular zone without high FLAIR (t126 = 3.9; P < 0.001) and control regions (t179 = 1.9; P = 0.046). Anisotropic q and fractional anisotropy values were lower in regions with high FLAIR compared with the subventricular zone without high FLAIR (t181 = 11.6, P < 0.001 and t184 =12.4, P < 0.001, respectively). CONCLUSION: DTI data showed that the subventricular zone is involved in glioblastoma with increased isotropic p values in the subventricular zone with high FLAIR, indicating tumor infiltration.