Study objective: To date, the study of critical illness in the emergency department has been limited. The purpose of this study was to determine the ED length of stay and procedures performed in medical critical care patients. Design: Descriptive study of a prospective single cohort. Setting: Large urban public hospital. Types of participants: Fifty consecutive ED patients subsequently admitted to the medical ICU. Measurements and main results: The study population consisted of 24 women and 26 men. The mean ED stay was 284.5±212.6 minutes (median, 255 minutes; interquartile range [IQR], 115 to 355 minutes). Patients remained in the ED after administrative transfer of their care to the medical ICU an average of 75 ±71.4 minutes (range, 10 to 375 minutes; median, 50 minutes; IQR, 25 to 105 minutes). Forty-one of these patients (82%) received one or more critical care procedures. The mean time to performance of first procedure was 92.8±180.6 minutes (median, 23 minutes; IQR, 11 to 82 minutes) from ED arrival. Death after ICU admission occurred in 11 patients. Mean ED length of stay was 291±269.8 minutes (range, 35 to 980 minutes; median, 135 minutes; IQR, 85 to 467 minutes) in nonsurvivors, and 91% of them received procedures in the ED. Survivors averaged 282.4±193.4 minutes (rnage, 15 to 230 minutes; median, 263 minutes; IQR, 126 to 355 minutes) ( P=NS) and 79.5% ( P=NS) received ED procedures. Conclusion: Critically ill patients spend a substantial amount of time in the ED before transfer to the ICU. Typical ICU procedures are commonly performed. Further study of the impact on patient outcome of ED stay and the procedures performed in critically ill medical patients should be conducted.