Two hundred thirty-eight patients admitted consecutively to a critical care unit through an emergency room were assessed prospectively for the presence of delirium. Thirty-eight patients (16%) developed delirium. Delirium occurred with equal frequency in all disease categories. The presence of abnormal head imaging which required medical intervention did not predict the development of delirium. The median delay between admission and the development of delirious was 4 days, however, one-fourth of the patients were delirious on the day of admission. The patients with abnormal head imaging who required medical intervention had a higher frequency of onset of delirium on the first day compared with patients without. The delirium lasted a median of 5 days and resolved within a week in over 70% of patients. These results confirm that delirium is frequently present in patients who require acute critical care after emergency room evaluation. In this population, serious medical disease is a better predictor of the development of delirium than the presence of abnormal brain imaging which required medical intervention. Although delirious patients have longer lengths of stay, the presence of delirium does not predict higher mortality, as has been reported in other populations. This could be because delirious patients admitted to the critical care unit through the emergency room have fewer premorbid medical problems predisposing them to poor outcome.