Background: Volunteer firefighters belong to a risk population regarding the development of posttraumatic stress disorder (PTSD). However, given the frequency of work-related trauma, PTSD prevalences seem relatively low. Protective factors appear to be effective and are the focus of this study. Objective: We investigated the PTSD-prevalence as well as the influence of trauma exposure and the impact of protective factors resilience and Sense of Coherence (SoC) on symptoms of PTSD in volunteer firefighters. Method: Data from 232 participants of an online questionnaire study were analysed using a path model approach. Results: 'The results suggest a possible prevalence of PTSD of 12.5% and 2.2% for partial PTSD based on self-report measures. SoC and trauma event load proved to be independent of each other, as no intercorrelations were found. But both directly predicted PTSD severity. Higher resilience scores predicted the participants' Sense of Coherence, but PTSD severity was only indirectly affected by resilience, which was entirely mediated by SoC. Further, although SoC and trauma load increase with age and years of job experience, it is only SoC that affects PTSD severity, not age or years of experience. Conclusions: The results emphasize that not only exposure to potentially traumatic events predicts the later probability of developing symptoms of PTSD, but that the integration of stressful experiences into the self-concept (associated with SoC) is essential for the development of PTSD. Future research should address the question of causality between SoC and PTSD, and consider which factors moderate the SoC.