Background: Dispatched citizen responders are increasingly involved in out-of-hospital cardiac arrest (OHCA) resuscitation which can lead to severe stress. It is unknown which psychological assessment tools are most appropriate to evaluate psychological distress in this population. The aim of this systematic review was to identify and evaluate existing assessment tools used to measure psychological distress with emphasis on citizen responders who attempted resuscitation. Methods: A systematic literature search conducted by two reviewers was carried out in March 2018 and revised in July 2018. Four databases were searched: PubMed, PsycInfo, Scopus, and The Social Sciences Citation Index. A total of 504 studies examining assessment tools to measure psychological distress reactions after acute traumatic events were identified, and 9 fulfilled the inclusion criteria for further analysis. The selected studies were assessed for methodological quality using the Scottish Intercollegiate Guidelines Network. Results: The Impact of Event Scale (IES) and The Impact of Event Scale-Revised (IES-R) were the preferred assessment tools, and were used on diverse populations exposed to various traumatic events. One study included lay rescuers performing bystander cardiopulmonary resuscitation and this study used the IES. The IES and the IES-R also have proven a high validity in various other populations. The Clinical administered PTSD scale (CAPS) was applied in two studies. Though the CAPS is comparable to both the IES-R and the IES, the CAPS assess PTSD symptoms in general and not in relation to a specific experienced event, which makes the scale less suitable when measuring stress due to a specific resuscitation attempt. Conclusions: The IES and the IES-R seem to be solid measures for psychological distress among people experiencing an acute psychological traumatic event. However, only one study has assessed psychological distress among citizen responders in OHCA for which the IES-R scale was used, and therefore, further research on this topic is warranted.