Introduction We aimed to determine the rate of preventable death in patients who died early and unexpectedly following hospital admission from the emergency department (ED). Methods We conducted a retrospective multicenter study in four centers from the Paris metropolitan area. Inclusion criteria were medical patients who died in hospital within 72 hours of ED attendance and were not admitted to the intensive care unit (unexpected death). Exclusion criteria were limitations of care determined by treating physicians. The existence of a limitation of care decision was adjudicated by two independent chart abstractors. Preventable death was defined as death occurring as a result of medical error. For each selected patient with unexpected death, charts were examined for medical errors and rated on a 1 to 5 preventability scale (from very unlikely to very likely) for the preventability of the death. The primary endpoint was the likely preventable death, rated as 4 or 5 on the preventability scale. Results We retrieved 555 charts; 47 unexpected deaths were analysed; 24 (51%) were considered as preventable. There was a median number of medical errors of two. The most common process breakdowns were incorrect choice of treatment (47% of patients) and failure to order appropriate diagnostic tests (38% of patients). The most common medical error was a severe delay or absence of recommended treatment for severe sepsis, which occurred in 10 (42%) patients. Conclusions In our sample, more than half of unexpected deaths are related to a medical error, and could have been prevented.