Objective: To determine the association between ED overcrowding and outcomes for critically ill patients Design and Setting: We included medical and surgical pts that all of them were intubated promptly to ED of 2 general hospitals of Athens GR, for 12 months. Pts survived > 24hours were divided into 2 groups: ED boarding < 6 hrs (group A) and ED boarding ≥ 6 hrs (group B). In the ED, 196 critically ill patients with a mean age 59.6±20.9 yrs and APACHE II score 24.6±12.7 were intubated. Results: Group A = 76 pts (mean time ED boarding, LOS, mortality): 28 pts were admitted to CCU (30.7±20.4, 7.7±9.3, 42.9%), 32 to ICU (231.25±103.1, 11.9±7.8, 37.5%) and 16 to intermediate unit (191.3±33.5, 7.8±5.7, 0%). Group B = 120 pts (mean time ED boarding, LOS, mortality): 28 pts were admitted to ICU (559.28±101.6, 15.6±10.3, 58.7%) and 92 to intermediate unit (3094.4±3273.4, 19.1±14.5, 78.3%). Hospital LOS was 19.2±20.4 days for group A vs 41.5±62.7 days for group B (P<0.001), and mortality 26.8% vs 45.7% respectively (P<0.001). Delayed admission, higher Apache II, age > 61 yrs, female gender and direct admission to ICU were associated with lower hospital survival (odds ratio 0.815; 95% 0.612-0.976). Conclusions: Boarding time of critically ill from ED to ICUs is very important because it is strongly related to the hospital LOS and mortality rate.