The current stipulation that headache must begin (or be reported to have begun) within 7 days of head injury (or awareness of the injury) is somewhat arbitrary. Some data suggest that headache may begin after a longer interval. In the following suggested diagnostic criteria, the maximal time interval between the head injury and headache onset is set at 3 months, but it is presumed that headaches that begin in closer temporal proximity to the injury are more likely to be accurately attributed to the injury. Future studies should continue to investigate the utility of these and alternative diagnostic criteria for A5.1 Acute headache attributed to traumatic injury to the head that allow for headache to begin beyond 7 days and up to 3 months after the injury.