Extragonadal germ cell tumours (EGGCTs) originated in prostate are extremely rare, with <20 cases described in the literature. We report a case of a patient with a primary prostatic mixed EGGCT. A 47-year-old man presenting severe low urinary tract symptoms and signs of prostatic enlargement, with no malignancy suspicion, underwent transurethral resection of the prostate. The histopathological evaluation suggested the diagnosis of a retroperitoneal sarcoma. The patient underwent neoadjuvant chemotherapy and then was submitted to radical cystoprostatectomy. Histology revealed a mixed EGGCT of the prostate with yolk sac tumour and seminoma components. No testicular abnormalities were identified on the postoperative scrotal ultrasound. The patient went through four cycles of chemotherapy with bleomycin, etoposide and cisplatin. After 12 months of follow-up, the patient is alive and free of recurrence.