The purpose of this study was to examine the role of several personality variables (empathy, comprehensibility, challenge and sense of humour) as moderators of the relationship of job demands (traumatic task and overload) with secondary traumatic stress. 175 emergency professionals of the Community of Madrid completed the Secondary Traumatic Stress Measure (STSM). The results of the hierarchical multiple regression analysis provide evidence for the moderator role of personality variables in the secondary traumatic stress process. Lastly, the discussion emphasises the need to focus on the interaction between personality and job demand variables in order to advance our understanding of the process of trauma in emergency professionals.