BACKGROUND: Emergency departments (EDs) are crowded with critically ill patients, many of whom are no longer able to communicate with the emergency staff. Substitute decision makers are often unknown or not reachable in time. The availability of advance directives (ADs) among Swiss ED patients has not yet been evaluated. The purpose of this prospective survey was to investigate the prevalence of ADs among ED patients and to identify factors associated with the existence or absence of ADs. METHODS: In a prospective survey, we enrolled consecutive patients from 10-30 July 2017 who visited a tertiary care ED. Patients completed a written, standardised and self-administrated questionnaire during the waiting time. The primary endpoint was the prevalence of ADs in ED patients. Secondarily, we defined predictors associated with the existence or absence of ADs. Two months after the first survey, there was a written follow-up survey asking patients without ADs whether they had completed an AD in the meantime. RESULTS: Fifty-eight of 292 enrolled ED patients (19.9%) had a completed AD. Overall, 49.3% of the survey population was female. Patients having an AD were older (69.5 years, interquartile range [IQR] 57-81 vs 39 years, IQR 27-56) and had more comorbidities (67.2% vs 38.9%) compared with patients without ADs. The four leading reasons given for not having an AD were: 33.6% never considered completing one, 26% did not know about ADs, 14% preferred family to make decisions, 11.6% felt it was too early to make such a decision. Predictors for having an AD were older age (p <0.001), being in long-term medical treatment by a specialist (p = 0.050), being Swiss (p = 0.021) and living with nursing care (p = 0.043). Of the ED patients with ADs, 46.6% discussed their AD with the family and 31% with their general practitioner. Results of the follow-up survey showed that eight participants had completed an AD in the meantime. The prevalence of ADs increased from 19.9% to 22.6%.DISCUSSION: During the last 20 years, the percentage of patients having an AD has not changed. Even today, only every fifth ED patient has a completed AD. Nearly two thirds of ED patients never considered completing one or did not know about ADs. Therefore, there is an urgent need to better inform and sensitise the public, so that they will define in a timely manner legally valid and specifically defined decisions about future medical treatments and wishes by completing individual directives.