We compared the plasma DNA concentrations in patients with different prostate cancer (PCa) stages and with benign prostate hyperplasia (BPH) and in healthy persons. Patients with localized cancer had DNA plasma within the reference interval. Increased plasma DNA was found in patients with lymph node and distant metastases and also in BPH. The association between plasma DNA and the survival time was similarly strong as with prostate-specific antigen. It can be concluded that plasma DNA has a limited validity as metastatic marker in PCa patients but follow-up studies combined with the investigation of tumor-related characteristics of plasma DNA would be reasonable.