The prediction of outcome is one of the major problems associated with traumatic brain injury. Recently, investigations have been performed on the potential use of circulating cell-free DNA in plasma for clinical diagnosis and prognosis of a variety of conditions. In this study, we investigated DNA plasma concentrations after severe traumatic brain injury (TBI) and its correlation with primary outcome. We studied 41 male victims of TBI, with isolated severe TBI or severe TBI with associated exracranial injuries. Control samples were obtained from 13 healthy male volunteers. Plasma DNA was measured by a real-time PCR assay for the beta-globin gene. The mean time for first sampling (study entry) was 11.7 +/- 5.2 h after injury; subsequent DNA determinations were performed 24 h after study entry. Mean plasma DNA concentrations were significantly increased in TBI patients (366,485 and 131,708 kilogenomes-equivalents/L, at study entry and 24 h later, respectively) compared with the control group (3031 kilogenomes-equivalents/L). Additionally, a significant correlation between higher plasma DNA concentrations, determined 24 h after study entry, and fatal outcome was observed. However, at second sampling, there was no significant correlation between plasma DNA concentrations and the presence of associated extracranial injuries. High plasma DNA concentrations at second sampling time predicted fatal outcome with a sensitivity of 67% and specificity of 76%, considering a cut-off value of 77,883 kilogenomes-equivalents/L. Thus, this study showed that severe TBI is associated with elevated DNA plasma levels and suggests that persistent DNA elevations correlate with mortality.