Background: Little is known about how pharmacists think and act in the situation when they need to prioritize patients without prioritization tools. Aim: To understand how Emergency Department (ED) pharmacists prioritize patients for medication review. Method: A multi-method study with pharmacists working in one ED in Denmark. At the start of the study, non-clinical prioritization rules had been implemented at the ED to ensure that medication histories were available quickly. Qualitative participant observations of all seven pharmacists who work at the ED were carried out. Semi-structured interviews with six of the pharmacists were held near in time to the observations. Observations for each pharmacists’ patients were analysed inductively looking for patterns and themes. The interviews were audiotaped, transcribed verbatim and analysed inductively. Results: The interviews shed light on the kinds of considerations pharmacists processed when prioritizing patients and how they used the ground rules (as set out in the PDSA process). The observations supplemented these data by showing some notable differences between pharmacists’ prioritization procedures that linked to their clinical experience. The interviews highlighted the importance of collaboration with physicians and how pharmacists could be better integrated in the ward team. Conclusion: Although the ward-established rules increased efficiency, they were handled differently by the pharmacists according to experience, and were not deemed helpful in detecting the clinically meaningful ED patients. A prioritization tool and sitting near to the physicians at the ward would enable pharmacists to become further integrated into patient care and improve prioritization of patients for medication reviews.