OBJECTIVE: The presence of posttraumatic amnesia (PTA) and loss of consciousness have been main factors used in a number of concussion guidelines. In this article, the focus is on using PTA (both retrograde and anterograde) as salient indicators of traumatic brain injury severity and the most reliable index of outcome prediction, even in mild cases. DATA SOURCES: A MEDLINE search for the years 1990-2000 using the key words posttraumatic retrograde and anterograde amnesia, concussion and mild traumatic brain injury was done. DATA SYNTHESIS: On-the-field testing of PTA is a salient and integral component of the initial and follow-up neurologic assessments of the head-injured athlete. CONCLUSIONS/RECOMMENDATIONS: Initial and follow-up assessments of PTA, anterograde and retrograde, are an essential part of the neurologic evaluation of the head-injured athlete. Increasingly, neuropsychological testing, including computer models, is being employed in this assessment. The importance of not just PTA but all postconcussion signs and symptoms being absent at rest and exertion before allowing the athlete to return to play is emphasized.