In order to identify an adverse event occurrence hazard ratio of 1.2 with a power of 0.9 during ED crowding, a cohort of 104,000 patients is needed. Therefore, data will be retrieved during a 2 year period during which the reviewer is blinded to the degree of ED crowding in relation to the findings on adverse events. The occurrence of adverse events and mortality will be compared to not crowded shifts, corrected for baseline risk factors. A carefully standardized admission form for registration of relevant information as well as a computerized search tool for screening for adverse events will allow finalizing this study within the foreseen time frame.