Triage, as a concept, is relatively new in Sweden and means 'sorting'. The triage process was developed to grade patients who needed immediate care. Triage is currently important for the emergency treatment system, and nurses are expected to work with it professionally. The aim of this study is to describe how nurses implement triage when patients arrive at the emergency department of a county hospital, situated in a rural area of Sweden, as well as to highlight the factors considered when prioritizing, in connection with nurses' decision-making. The method used was observations of 19 nurses, with minimal disturbance in their triage work, followed by a short tape-recorded interview, during which the nurses were asked to reflect upon their decision of priorities. Qualitative content analysis of data has been used. The results were divided into two areas, internal factors and external factors. The internal factors reflect the nurse skills and personal capacity. The external factors reflect work environment, including high workload and practical arrangements, and should always be perceived and taken into consideration. Using these factors as a basis, the patients' clinical condition, clinical history, various examinations and tests form an assessment, which subsequently results in a prioritization.