Patient safety is an internationally recognised health care priority with up to 17% of hospital admissions resulting in an adverse event (AE; unintended harm from health care provided). One million people present to New Zealand’s emergency departments (ED) every year. Due to the variety of cases, case complexity and need for speed in providing care to emergency patients, EDs have been described as a ‘natural laboratory for error.’ Despite this, there are no current data on the number or cause of AEs in New Zealand’s EDs. There is a compelling need for a contemporary prospective study examining New Zealand’s ED AEs. The proposed study will address this gap in our knowledge about patient safety and provide important information on the frequency, severity and preventability of AEs. With implementation into ED safety campaigns, guidelines and national dissemination, this new information will improve the safety of ED care for all New Zealanders.