Critical workplace events (e.g., assaults), chronic stressors, burnout, and work conditions all affect nurse well-being. The present study investigated associations among these sources of stress and posttraumatic stress disorder (PTSD) symptoms in psychiatric nurses, hypothesizing that burnout would mediate the paths between workplace stressors and PTSD. Surveys were completed by 611 psychiatric nurses or allied health staff working on inpatient units in three psychiatric hospitals. Participants reported on critical events and chronic stressors specific to providing psychiatric care and completed the Maslach Burnout Inventory (MBI), Areas of Worklife Survey (AWS) (work conditions), and PTSD Checklist for DSM-5. Data were analysed using structural equation modelling. Burnout had a direct relation to PTSD symptoms and partially mediated the effect of exposure to critical events, but not chronic stressors, on PTSD symptoms. Chronic stressors related to patients' disturbing behaviour (e.g., flooding room, eating non-food items) had a direct effect on PTSD symptoms, but those related to resisting care (e.g., screaming constantly, physically resisting care) had no significant association. Worklife conditions had a negative direct effect on Burnout and indirect effect on PTSD, whereby participants reporting poorer alignment of work conditions with their expectations had higher Burnout and PTSD symptom scores. Different sources of workplace stress have different relations to PTSD symptoms, and Burnout has both direct and mediation effects. Interventions aimed at reducing patients' aggressive and disturbing acts and improving healthcare providers' burnout and worklife factors in hospitals may all be needed to reduce PTSD among psychiatric staff.