Testicular metastases from prostate cancer (PCa) are exceedingly rare and are typically accompanied by other metastatic sites. We present the case of an 82-year-old male patient who developed isolated testicular metastasis 15 years after undergoing radiotherapy and androgen deprivation therapy (ADT) for localized PCa. The patient presented with a palpable left testicular mass, which was confirmed to be a metastatic prostate adenocarcinoma by histopathological and immunohistochemical analyses. Orchiectomy was performed for both diagnostic and therapeutic purposes, resulting in a significant decline in serum PSA levels. The patient continued ADT with regular monitoring, and no further metastases were detected. This case highlights the importance of long-term surveillance and advanced diagnostic techniques for detecting the rare metastatic presentations of PCa. Although isolated testicular metastases may have a better prognosis than other metastatic patterns, optimal postorchiectomy management remains uncertain, underscoring the need for further research and a multidisciplinary approach.