Prostate specific membrane antigen (PSMA) positron emission tomography (PET) is an emerging imaging modality in prostate cancer. However, 68 Ga-PSMA-PET may also have diagnostic utility in the setting of renal cell carcinoma (RCC). We investigate the differential role of 18 F-fluorodeoxyglucose (FDG) and PSMA-PET/CT scanning in patients with oligometastatic RCC. In particular, we focus on the utility of PSMA-PET for diagnostic evaluation of isolated or limited metastases planned for local surgery or radiation, as well as the potential utility of PSMA-PET for therapeutic response assessment in patients receiving stereotactic ablative body radiotherapy (SABR).We present a retrospective series of eight patients in which comparative imaging modalities are evaluated against PSMA-PET scanning. FDG-PET and PSMA-PET scans were performed prior to definitive treatment (either surgery or SABR) of limited recurrent disease. Response assessment after SABR was performed with both PET imaging modalities at multiple time points in a subset of four patients.Prostate specific membrane antigen uptake is typically more intense than FDG in RCC. In all but two cases, one of which was papillary carcinoma, FDG-PET and PSMA-PET are concordant for detection of sites of disease. We demonstrate for the first time the differential kinetics of post-treatment response using PSMA and FDG-PET, with a more rapid metabolic response observed on FDG-PET. Both modalities demonstrate response earlier than morphological appearances on CT or MRI imaging.Our series suggests that PSMA shows early promise as a diagnostic and therapeutic response assessment tool in patients with metastatic RCC receiving definitive local therapies.