Mild Traumatic Brian Injury (mTBI) is a common diagnosis and approximately one third of mTBI patients experience a variety of cognitive, emotional, psychosocial and behavioral post-concussion symptoms. When a cluster of these symptoms persists for more than three months they are often classified as post-concussion syndrome (PCS). The objective of this study was to determine prevalence rates, risk factors and functional outcome associated with PCS six months after mTBI applying divergent classification methods. Follow-up questionnaires at six months after mTBI included the Rivermead Post-Concussion Symptoms Questionnaire (RPQ) and the Glasgow Outcome Scale Extended (GOSE). The RPQ was analyzed according to different classification methods: the mapped International Classification of Diseases (ICD-10)/Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), the RPQ total score, the RPQ3 and the three-factor model using two different cut-off points (mild or worse and moderate or worse). Our results from a sample of 731 mTBI patients showed that prevalence rates of PCS ranged from 11.4% - 38.7% using divergent classification methods. According to all eight methods, 6.3% (N=46) of mTBI patients experienced PCS. Applying the divergent classification methods resulted in a different set of predictors being statistically significantly associated with PCS and a different percentage of overlap with functional impairment, measured with the GOSE. In conclusion, depending on the classification method and rating score used, prevalence rates of PCS deviated considerably. For future research, consensus regarding the diagnostic criteria for PCS and the analysis of the RPQ should be reached, to enhance comparability of studies regarding PCS after mTBI.