A 69-year-old man presented with an incidental undifferentiated carcinoma of the prostate. Ten years ago the patient had clinical stage I seminoma of the right testis with adjuvant radiotherapy. Follow-up care was without pathological findings. Staging examinations did not show metastatic disease. After radical prostatectomy with pelvic lymphadenectomy, the histological examination revealed a metastatic seminoma in the prostate. Therefore, the diagnosis was a late relapse in an extremely rare location. So far only four other reports describe testicular seminoma with metastases to the prostate.