Introduction: Guidelines are important for guiding clinical practice and governing registered nurses’ work in an emergency room to enable them to secure quality of care and patient safety in a life-saving situation. However, guidelines are not always systematically prepared, or evidence based. This study aimed to map and describe the content of Swedish guidelines governing the registered nurses’ work in emergency rooms. Methods: A descriptive cross-sectional design, together with a thematic synthesis of content of the submitted guidelines. The data were analyzed with descriptive statistics and a thematic synthesis. Quality of the guidelines was measured using a modified version of the AGREE II instrument. Results: The result is based on 190 included guidelines, collected from 37 participating emergency departments. The registered nurses’ work in emergency rooms was guided by an instrumental and task-oriented approach to care, with a wide variation in how the registered nurses’ work was described in the guidelines. The quality of the guidelines was poor. The registered nurse was reported as target user in 15 % (n = 29) of the guidelines. None of the guidelines described the population to whom they were meant to apply. In 17 % (n = 32) there was an explicit link between recommendations and supporting evidence. Conclusions: There is a need to improve guidelines to support registered nurses in assessing, treating, and providing fundamental care for patients with life-threatening illnesses in an equal, evidence-based, and person-centered way. Registered nurses should play an active role in the development of the guidelines governing their work.