There has been an increase in violence and aggression in emergency departments (EDs) in recent years. Among professional health care workers, nurses are more likely than other staff members to be involved in aggressive incidents with patients or relatives. This research study was undertaken to determine nurses' perceptions of the factors that cause violence and aggression in the ED. Using a qualitative approach, twelve nurses working in an Irish ED were interviewed. Thematic analysis of the interview data revealed that environmental and communication factors contributed to violence and aggression in the ED. Participants perceived waiting times and lack of communication as contributing factors to aggression, and triage was the area in the ED where aggression was most likely to occur. A number of key recommendations arise from the study findings and they all relate to communication. To address the aggression that may arise from waiting times, electronic boards indicating approximate waiting times may be useful. Also, information guides and videotapes on the patient's journey through the ED may be of benefit. Consideration to the appointment of a communication officer in the ED and communication training for ED staff is also recommended. (C) 2013 Elsevier Ltd. All rights reserved.