Temozolomide-based radiochemotherapy (RCT) is a treatment standard for glioblastoma patients. However, RCT is associated with risks of neurocognitive decline. Perfusion is a possible early marker of tissue damage and has been shown to correlate with cognitive changes in many diseases. Perfusion decrease at 3 to 6 months after RT was recently reported in glioblastoma patients. However, it remains unclear whether the decrease is reversible and thus possibly a precursor of the late-delayed cognitive changes. In this study, we have measured perfusion changes up to 18 months following RCT. No further progress of perfusion deficits was found indicating that the early perfusion decrease is predictive of late perfusion decrease and might thus be connected with cognitive decline.