Interruptions are inevitable in the clinical environment, and they have been linked to an increased risk of diagnostic errors by radiologists and medication administration errors by nurses. However, the effects of interruptions are not predictable and many interruptions are essential for proper patient care. Recognizing this, commentators have called for research to analyze the causes and effects of interruptions, rather than attempting to categorically prevent interruptions. This study, conducted in an academic emergency department, contributes to our understanding of how interruptions influence patient care by examining the effect of interruptions on several specific nursing tasks. Interventions that were interrupted took longer than uninterrupted tasks, and interruptions were a significant contributor to overall nursing workload. Patients and families were the most frequent source of interruptions, demonstrating that simply implementing interventions to prevent interruptions could cause unintended consequences. The state of patient safety in the emergency department, including the role of interruptions, is discussed in a past AHRQ WebM&M perspective.