Their utility in the diagnosis of mild to moderate TBI is still unknown. The majority of mild brain injuries recover spontaneously. However, 10–20% of mTBI patients continue to suffer from post concussive syndrome. Therefore, it is important to establish diagnostic marker that can distinguish patients with a head injury regardless of the severity of the injury as well as distinguish individuals based on severity of mTBI. MicroRNAs, which are small non-coding endogenous RNA, have shown great promise as diagnostic markers of several diseases and disorders. Unique changes in the expression of miRNAs in the brain samples after TBI have been reported. Redell and group have also investigated the diagnostic potential of the miRNA in severe TBI. To date, a comprehensive evaluation of miRNA as a diagnostic biomarker of mTBI, which also addresses the heterogeneous nature of mTBI, has not been described. The present study was designed to identify serum miRNAs as biomarkers of mild brain injury, which could identify the occurrence of mTBI independent of the severity of the injury within the mild spectrum of TBI. In this study, a previously described free-fall weight-drop model of mTBI with modifications was used to study the neurobehavioral deficits over a period of 30 days and miRNA modulation during the acute phase of injury. This model resembles the blunt head trauma resulting from a vehicle crash, combat, falls, and other recreational activities. Mice were subjected to an increasing grade of injury within the mild spectrum by varying the weight and height of the falling metal rod, with the most severe being a 3 cm fall height combined with a 333 g weight. The neurobehavioral severity scale-revised was measured at day 1 post injury, along with open field locomotion activity and acoustic startle responses. NSS-R scores correlated and increased significantly with the grade of injury. OFL activity and startle responses were reduced in the injury groups, except the 2461g/2 cm injury. OFL and ASR activity returned to normal levels by day 14 post injury and remained constant through day 30 post injury measurements. To determine the miRNA changes in the serum during the acute phase of injury, miRNA arrays were LDN-193189 performed on serum RNA isolated at 3 hr post injury. Thirteen miRNAs showed similar expression changes among injured mice compared to sham controls. Bioinformatics analyses using the Ingenuity Pathway Analysis and DNA Intelligent Analysis -miRPath software showed that the number of significantly modulated serum miRNAs predicted to be involved in brain related functions increased with the severity of the injury. MTBI is a heterogeneous injury that can range from no clinical symptoms to development of post concussive syndrome after injury. Rapp and Curly describe mTBI as an event that may lead to the development of neurological disorders. The heterogeneous nature of mTBI makes it difficult to diagnose, based exclusively on current behavioral and neurocognitive analyses.