The prevalence of postconcussional disorder (PCD) is not exactly known.  Inconsistency in the definition and classification of PCD has made the epidemiology of the disorder difficult to describe accurately. However, research suggests that 10 to 20% of individuals who suffer a concussion go on to develop postconcussional disorder symptoms. 

There are also problems with data collection for postconcussional disorder.  Many people who may have suffered a mild traumatic brain injury may not go to the hospital.  For those that do, proper documentation may not be made due to the lack of external injuries present and the patient will be discharged without any contribution to data for epidemiological studies.

***Note:  There are relatively few good epidemiological studies on the incidence of mild traumatic  brain injury and the incidence of traumatic brain injury is controversial (Silver, McAlister, & Yudofsky, 2005).