Approximately 28,000 service members (SMs) sustain a traumatic brain injury (TBI) each year in the U.S. military. The majority of the injuries result either in a brief or no loss of consciousness, and are classified as a mild TBI (mTBI or concussion). Current evaluation guidelines of SMs suspected of having a mTBI rely heavily on self-reports. However, there is concern that SMs typically minimize or do not report their symptoms of mTBI for fear that doing so will result in being removed from the battlefield. Because mTBI often results in headaches, cognitive dysfunction, attention difficulties, and balance problems, returning to the battlefield before resolution of their symptoms can be dangerous for the SM and for their unit. Sustaining a second concussion before resolution of a previous mTBI also may make long-term neuronal injury more likely. The mTBI Diagnostics Workshop was designed as a forum where civilian and military experts from a variety of TBI-related clinical and basic science disciplines could meet to define the diagnostic tools, alone or in combination, that were most likely to result in an acute, objective diagnosis of mTBI. The premise of the meeting was that a small number of well-focused research projects conducted over the next 2-3 years could be done to validate the optimal test, or more likely combination of tests, that would be practical and reliable for the acute diagnosis of mTBI within 2-3 h of injury in theater. The recommendations of the Workshop are provided in this report.