Prostate-specific membrane antigen (PSMA) is a transmembrane enzyme also known as folate hydrolase 1 highly expressed by prostate cancer (PCa) cells. However, PSMA overexpression by tumor-associated neovasculature of a variety of solid tumors, including glioblastoma (GBM), has also been proven. This clinical case reports about a 67-year-old man with a history of PCa who underwent radical surgery for GBM and performed a Ga-PSMA-11 PET/CT to restage PCa. PET imaging showed PSMA uptake in GBM residual disease after surgery. This finding suggests a possible role of PSMA inhibitors as diagnostic and therapeutic agents in patients affected by GBM.