Biochemical recurrence of prostate cancer (PCa) after curative radiotherapy is defined as a prostate-specific antigen (PSA) rise of ≥2 ng/ml above the nadir ("Phoenix criteria", 2005). With the introduction of prostate-specific membrane antigen positron emission tomography (PSMA-PET), the ability to localise PCa recurrences has increased markedly. Here, we reviewed 315 patients scanned with PSMA-PET after curative radiotherapy in the Prostate Cancer Network Amsterdam (2015-2018). Sixty-three patients (20.3%) were scanned below the Phoenix threshold (PSA rise <2.0 ng/ml). In 53 of these patients (84.1%), PSMA-PET-avid lesions were detected nonetheless: 21 patients (33.3%) revealed a local recurrence as a single site of disease, 32 patients (50.8%) harboured metastatic PCa. Besides rising PSA, no predictors were identified that prompted early PSMA-PET imaging. In this communication, we report on the frequent detection of metastatic PCa with PSMA-PET in men below the Phoenix PSA threshold. These findings are a plea for re-evaluation of current diagnostic work-up for rising PSA values after radiotherapy, as early detection of recurrences might refine salvage and/or adjuvant therapies. PATIENT SUMMARY: This study reports on the unexpected detection of prostate cancer (PCa) recurrences with prostate-specific membrane antigen positron emission tomography in patients treated with radiotherapy. This calls for re-evaluation of the current criteria for recurrent PCa after radiotherapy.