The WHO Collaborating Centre for Neurotrauma Task Force on Mild Traumatic Brain Injury performed a comprehensive search and critical review of the literature published between 1980 and 2002 to assemble the best evidence on the epidemiology, diagnosis, prognosis and treatment of mild traumatic brain injury. Our primary sources of literature were Medline, Cinahl, PsycINFO and Embase. Citations were screened for relevance to mild traumatic brain injury, using a priori criteria, and relevant studies were critically reviewed for scientific merit. We identified 38,806 citations, of which 671 studies were judged relevant to the mandate of the task force. These, plus 70 studies found by hand-searching reference lists and 2 original research reports performed as part of the task force mandate were subjected to critical reviews. After review, 313 (42%) were accepted on scientific merit and comprise our best-evidence synthesis. Ninety percent of the literature on mild traumatic brain injury was found in Medline and another 5% in PsycINFO.