An 82-year-old man underwent radiotherapy (brachytherapy, external beam radiotherapy) for prostate cancer, followed approximately five years later by endocrine therapy for biochemical recurrence, which controlled the prostate-specific antigen (PSA) level. His later admission due to severe gross hematuria and dysuria is described. Computed tomography and magnetic resonance imaging findings revealed a cystic tumor continuous with the prostate between the prostate and rectum, and this tumor was thought to be the cause of the hematuria and dysuria. Transrectal biopsy and transurethral resection of the prostate were performed for pathological diagnosis and improvement of dysuria. The pathological diagnosis was remnant prostate cancer, and the cystic tumor was thought to have developed as a result of prostate cancer recurrence. Although chemotherapy using docetaxel was considered postoperatively, the patient refused this treatment. Even though the PSA level was under control, the patient's condition progressed rapidly, with onset of pulmonary and cervical lymph node metastases within a short period of time, and the patient subsequently died.