Approximately 75% of traumatic brain injuries (TBI) are classified mild (mTBI). Despite the high frequency of mTBI, it is the least well studied. The prevalence of mTBI among service personnel returning from Operations Iraqi Freedom (OIF) and Enduring Freedom (OEF) and the recent reports of an association between repeated mTBI and the early onset of Alzheimer's and other types of dementias in retired athletes has focused much attention on mTBI. The study of mTBI requires the development and validation of experimental models and one of the most basic requirements for an experimental model is that it replicates important features of the injury or disease in humans. mTBI in humans is associated with acute symptoms such as loss of consciousness and pre- and/or posttraumatic amnesia. In addition, many mTBI patients experience long-term effects of mTBI, including deficits in speed of information processing, attention and concentration, memory acquisition, retention and retrieval, and reasoning and decision-making. Although methods for the diagnosis and evaluation of the acute and chronic effects of mTBI in humans are well established, the same is not the case for rodents, the most widely used animal for TBI studies. Despite the magnitude of the difficulties associated with adapting these methods for experimental mTBI research, they must be surmounted. The identification and testing of treatments for mTBI depends of the development, characterization and validation of reproducible, clinically relevant models of mTBI.