Objective: The aim of this study was to investigate the moderating role of prison personnel’s years of service working within a prison environment, on the relationship between the three trauma factors (self-harm/death, violent, environmental) measured by the Prison Personnel Trauma Measure (PPTM) and PTSD symptomology. Method: A non-probability convenience sample of 1995 Prison Personnel in the UK completed the Prison Personnel Trauma Measure (PPTM), Hospital Anxiety and Depression Scale (HADS) and the Posttraumatic Stress Disorder Checklist Version 5 (PCL-5). Results: Differential associations were identified between years of service, trauma and PTSD. Results showed specifically that years of service significantly moderated the relationship between violent trauma exposure and PTSD. Furthermore, it was identified this moderation occurred specifically in male personnel with higher years of service but not in female personnel. Years of service was not found to moderate the relationship between self-harm/death or environmental trauma exposure and PTSD in male or female personnel. Conclusion: The findings clarify linkages among years of service, trauma and PTSD, and elucidates which types of trauma exposure may be moderated by years of service within a prison environment. Implications for PTSD symptomology development are discussed. It is also suggested that future studies may advance the understanding of the mechanisms of the relationship between trauma exposure in prison and potential moderating factors on the development of PTSD, Anxiety, and Depression.