Objectives: Out-of-hours (OOH) services provide access to healthcare outside normal office hours, but the waiting time can sometimes be long. All callers must wait in the telephone queue, even if the health problem is urgent or life-threatening. We tested an emergency access button (EAB), which allowed callers with perceived severe health problems to bypass the queue. We aimed to investigate the severity of the health problems and the relevance of EAB use (assessed by triage professionals). Additionally, we aimed to calculate the number of suspected acute myocardial infarctions (AMI) and ambulance dispatches. Design: Descriptive study of a randomized intervention. Setting: OOH services in two major Danish healthcare regions. Subjects: 217,510 callers participated; 146,355 were randomized to intervention, and 6554 of 6631 (98.8%) questionnaires were completed by OOH triage professionals. Intervention: An EAB allowing randomly selected callers to bypass the telephone queue. Main outcome measures: Severity of contact and relevance of EAB use. Number of suspected AMIs and ambulance dispatches. Results: In both settings, contacts with EAB use concerned significantly more severe health problems than contacts without EAB use (p < 0.001). Triage professionals rated EAB use as "not relevant" in 23% of cases. Significantly more EAB users (10.4%) than EAB non-users (3.3% with EAB option and 1.7% without EAB option, p < 0.001) had a suspected AMI. Conclusions: We found higher proportions of severe health problems, suspected AMIs, and ambulance dispatches among EAB users. Only 23% of EAB use was rated "not relevant". This suggests that the EAB is used as intended. Key points Out-of-hours healthcare is challenged by increasing demand and long triage waiting times. An emergency access button may allow severely ill callers to jump the queue. Callers who bypassed the queue were more severely ill than callers who did not bypass the queue. Only 23% of bypassers presented "not relevant" health problems according to the triage staff.Trial registration: Identifier NCT02572115 registered at Clinicaltrials.gov on 5 October 2015.