A 78-year-old Japanese man who had undergone total prostatectomy for prostate cancer (pT3cN1M0, Gleason score 3 + 3) 20 years previously was referred to the Respiratory Medicine Department of our institution because of a 1-week history of chest pain and cough. Computed tomography showed multiple small nodules and mediastinal lymph node enlargement. Bronchoscopy revealed multiple soft polypoid masses and obstruction of the lingular segment. Prostate-specific antigen (PSA) concentrations had increased markedly from 0.48 ng/mL in 2014 to 741 ng/mL in 2018. The diagnosis of prostatic cancer metastases was confirmed by revealing the presence of PSA via immunohistological staining of a bronchoscopically obtained biopsy of one of the masses. The patient had not been attending scheduled follow-up visits for the past 4 years. Treatment with degarelix (a gonadotropin-releasing hormone) was started, and the PSA concentration decreased dramatically (29 ng/mL). Metastases from prostate cancer are rarely first diagnosed two decades after radical prostatectomy. This patient illustrates the importance of obtaining a complete medical history.