Abstract Background Emergency Departments (EDs) are important arenas for the detection of unhealthy substance use. Screening, Brief Intervention, and Referral to Treatment (SBIRT) for unhealthy alcohol use has been used in some ED settings with funding support from external sources. However, widespread sustained implementation is uncommon, and research aimed at understanding culture as a determinant for implementation is lacking. This study aims to explore cultural practices concerning the handling of patients with unhealthy alcohol use admitted to an ED. Methods An ethnographic study was conducted in an ED in the Capital Region of Denmark. The data consists of participant observations of Health Care Professionals (HCPs) and semi-structured interviews with nurses. Data was collected from July 2018 to February 2020. A cultural analysis was performed by using Qualitative Content Analysis as an analytic tool. Results 150 h of observation and 11 interviews were conducted. Three themes emerged from the analysis: (1) Setting the scene describes how subthemes “flow,” “risky environment,” and “physical spaces and artefacts” are a part of the contextual environment of an ED, and their implications for patients with unhealthy alcohol use, such as placement in certain rooms; (2) The encounter presents how patients’ and HCPs’ encounters unfold in everyday practice. Subtheme “Professional differences” showcases how nurses and doctors address patients’ alcohol habits differently, and how they do not necessarily act on the information provided, due to several factors. These factors are shown in remaining sub-themes “gut-feeling vs. clinical parameters,” “ethical reasoning,” and “from compliance to zero-tolerance”; and (3) Collective repertoires shows how language shapes the perception of patients with unhealthy alcohol use, which may cause stigma and stereotyping. Subthemes are “occupiers” and “alcoholic or party animal?”. Conclusions Unhealthy alcohol use in the ED is entangled in complex cultural networks. Patients with severe and easily recognizable unhealthy alcohol use—characterized by an alcohol diagnosis in the electronic medical record, intoxication, or unwanted behavior—shape the general approach and attitude to unhealthy alcohol use. Consequently, from a prevention perspective, this means that patients with less apparent unhealthy alcohol use tend to be overlooked or neglected, which calls for a systematic screening approach.