Firefighters commonly encounter traumatic events during duty hours. The purpose of this study was to investigate the characteristics of duty‐related trauma as risk factors for posttraumatic stress disorder in professional firefighters. A sample of 212 firefighters participated in the study and completed self‐reported questionnaires. Potentially traumatic events (PTE) were assessed using a list of 17 traumatic event types. The posttraumatic stress symptoms (PTSS) were measured by the Impact of Event Scale‐Revised (Lim et al., 2009; Weiss, 2007). A higher score for the composite index, which reflects both multiple PTE and peritraumatic suffering, increased the odds for significant PTSS after adjusting for age, sex, marital status, education, numbers of years worked, childhood trauma, and depressive symptoms (adjusted odds ratio [AOR] = 2.26, p = .001, Cohen's d = 0.20). Furthermore, indirect (AOR = 1.93, p = .009, Cohen's d = .16) and colleague‐related PTE (AOR = 1.97, p = .037, Cohen's d = .16) showed significant associations with PTSS. It is noteworthy that the combination of multiple PTE and peritraumatic suffering was more predictive of PTSS than either factor alone. Our findings also suggest that daily work exposure to indirect PTE may contribute to the occurrence of PTSS among professional firefighters.