Objectives and Background Measurements of patients' perceptions have been recognised as an important part of evaluations of the quality of care. However, in the Netherlands a standardised and validated instrument to systematically measure how patients experience the healthcare delivered in an emergency department (ED) is lacking. Therefore, we developed the Consumer Quality Index for the Emergency Department (CQI ED). Methods The CQI ED was developed according to the national CQI guideline. First, qualitative research was used to construct the CQI ED. Second, to assess psychometric characteristics the 84-item CQI ED, temporarily extended with 50 important questions, was sent to 653 patients who attended a large-sized ED in the Netherlands in January 2010. Exploratory factor analyses were used to determine the domains of the questionnaire. Improvement scores were computed by multiplying the importance scores with the percentages to the negative answering categories of the experience questions. Results Survey data of 304 (47%) patients were used for analyses. The first exploratory factor analysis resulted in 15 items grouped in three internally consistent domains: Attitude of the healthcare professionals, environment and impression of the ED and respect and explanation towards the patient. The second analysis, ignoring the general CQI guidelines, included 27 items and resulted in 5 domains: Attitude of the healthcare professionals, information and explanation, environment of the ED, leaving the ED, and general information and rapidity of care. The three most important aspects in healthcare performance at the ED were: trust in the competence of the healthcare professionals, hygiene at the ED and received care as expected. The highest improvement scores were mostly about informing patients. Conclusions The CQI ED is a reliable instrument to measure patients' experiences with care at the ED and seems applicable for local quality improvement. Preferring a construct of three or five domains depends on the choice for a ...