Objective: This study aimed to estimate the prevalence of traumatic brain injury (TBI) in a French prison population of young offenders and to study variables known to be associated with TBI. It also aimed to study whether TBI was associated with younger age at entry into prison; longer period of custody and re-offending. Participants: All young offenders (from 13 to 21) consecutively admitted to Fleury- Mérogis prison over a period of 3 months were included. Method: During the ad- mission procedure, young offenders were interviewed by healthcare staff using a self-reported questionnaire. Comparisons between cases (TBI +) and controls (TBI −) were performed. Results: Three hundred thirty two young offenders were included. The prevalence of self-reported TBI was 24.5%. The first cause of TBI was violence- related outcomes (25%). No differences were found regarding the number of times in custody and the total time spent in prison during the preceding five years. Cases accumulated multiple health problems including mental health problems (16.3% vs. 4.9%; p = .002) and a regular use of cannabis (28.7% vs. 15.9%; p = .02). Conclusions: The results provide further evidence that specific measures need to be developed such as, first of all, screening for TBI and related impairments upon arrival in prison.