Background: Workplace violence is a regular feature of emergency departments (ED) and reported to be increasing in frequency and severity. There is a paucity of data from regional EDs in Australia. The aim of this study was to identify the perpetrator and situational characteristics associated with security alerts in regional emergency departments. Methods: This retrospective descriptive study was conducted in two regional Australian hospital EDs. All incident reports, hospital summary spreadsheets, and patient medical records associated with a security alert over a two-year period (2017 - 2019) were included. The situational and perpetrator characteristics associated with security alerts in the ED were recorded. Results: One hundred fifty-one incidents were reported in the two-year period. Incidents most frequently occurred on late shifts and in an ED cubicle. Most incidents included multiple disciplines such as ED staff and paramedics, police and psychiatric services. One hundred twenty-five incidents had sufficient information to categorise the perpetrators. Mental and behavioural disorders (MBD) were the most frequent perpetrator characteristic present in security alerts (n = 102, 81.6%) and were associated with increased severity of incidents. MBDs other than psychoactive substance use (PSU) were associated with 59.2% (n = 74) of incidents and 66.7% (n = 18) of injuries. PSU was associated with 42.4% (n = 53) of incidents. Following PSU and MBDs other than PSU, repeat perpetrators were the next most prominent perpetrator category (24.8% n = 31) and were almost always associated with an MBD (93.5% n = 29). Conclusions: Violence incidents in the ED are often complex, patients present with multiple issues and are managed across disciplines. Interventions need to extend from one size fits all approaches to targeting specific perpetrator groups. Since MBDs are one of the most significant perpetrator factors, interventions focussing on this characteristic are needed to address workplace violence in EDs.