An 81-year-old man received androgen deprivation therapy for a locally advanced prostate cancer and, 6 months later, a curative radiation therapy. Half a year later, the patient presented with a steeply increased PSA value (32 ng/mL) and a suppressed testosterone level (0.48 nmol/L). The consecutively performed 68Ga-PSMA PET/CT revealed, besides local tumor remains and several PSMA-positive lymph node and soft tissue metastases, an extensive, diffuse PSMA ligand accumulation in the omentum, which was immunohistochemically proven to be a carcinomatosis of prostate cancer. None of the extraprostatic lesions were present in the pretherapeutic PSMA PET 1 year ago.