Study Object: To date, the study of critical illness in the emergency department has been limited. The purpose of this study was to determine the length of stay and procedures performed on critical care patients in ED, and to be help to estabilish Emergency physicians' education program. Method: We reviewed patient s medical record, who visited ED, Korea Univ. Hospital from Jan. 1996 to Jun. 1996 and admited to ICU. We analyzed data to age, sex, clinical diagnosis, length of stay, and critical procedures in ED. Results: The 12,721 patients visited ED during the study period, the 441 of 12,72l (3.50%) patients admited to ICU. 56 patients were excluded whose medical re cords were incomplete. The study populations consisted of 165 women and 220 men. The mean age were 52 year old (median, 58 year old). The mean length of stays were 606.1 (1445.9 minutes ( median, 180 minutes). One hundred sixty one of these patients 41.8 %) received one or more critical procedures. The medical critical patients were 252 cases, and surgical critical patients were 133 cases. The mean length of stay of medical critical patients was 738.8 (1748.9 minutes (median, 177.5 minutes) in medical department, 44.0% of them received critical procedures in ED. The surgical critical patients averaged 354.9 (410.7 minutes (median, 190 minutes) and 37.6% received critical procedures. Conclusion: Critical ill patients stay in the ED with a substantial amount of time, before admition to the ICU. Critical ill patients who have hemodynamiccal unstable conditions, compromized cardiopulmonary functions, and neurologic deficities, were managed in ED frequntly. Typical critical care procedures are commonly performed by emergency physicians. Therefore, I@t is important for emergency physician to prepare to critical ill patients.