Background: Professionals working in the emergency department (ED) are regularly exposed to traumatic events. Rates of posttraumatic mental health conditions vary widely in the literature and there is no agreement that rates in ED staff are elevated relative to other populations. Objective: We conducted a systematic review of international literature reporting prevalence of posttraumatic stress disorder (PTSD), depression, and anxiety in ED personnel to determine whether prevalence is elevated compared to the general community, and to evaluate convergent evidence across the literature for predictive factors. To our knowledge, there is no comprehensive review on this topic in the literature at this time. Methods: Seven databases were searched for studies reporting rates of PTSD, depression, and anxiety in ED personnel. Two independent researchers screened studies and assessed quality using Munn's Prevalence Critical Appraisal Instrument. Best-evidence synthesis determined whether conditions demonstrated elevated prevalence compared to the general population of Canada, a conservative benchmark. Results: Twenty-four studies from 12 countries and a combined sample size of 4768 were included. PTSD rates ranged from 0% to 23.6% (mean 10.47%), depression ranged from 0.7% to 77.1% (mean 24.8%), and anxiety rates ranged from 2.4% to 14.6% (mean 9.29%). Each condition was elevated compared to the general population. Sociodemographic variables were not consistent predictors. Elevated PTSD seemed most strongly related to workplace exposure and maladaptive coping. Conclusions: ED professionals have an elevated risk of experiencing PTSD, depression, and anxiety. Identification of organizational and workplace predictors are needed to inform interventions that will reduce risk and provide optimal treatment and management of PTSD, depression, and anxiety in ED settings.