A 62-year-old man with recently diagnosed prostatic adenocarcinoma was referred for a whole-body Ga-prostate-specific membrane antigen (PSMA) PET/CT scan for staging. Although the scan did not reveal metastatic disease, it did reveal a PSMA-avid lesion in the upper abdomen located between the liver and the stomach. Histopathologic examination demonstrated a gastrointestinal stromal tumor. The lesion demonstrated increased uptake in the margins of the tumor with a central photopenic area, which we consider to be the typical pattern on PSMA images of a gastrointestinal stromal tumor, based on theoretical PSMA distribution in such a tumor and other reported cases.