Many patients admitted for observation to the intensive care unit after a drug overdose do not ultimately require intensive care interventions. We retrospectively analyzed data on 209 overdose cases to determine whether clinical assessment in the emergency room could identify patients at risk for complications. Patients were classified as low risk when none of the following high-risk criteria were present in the emergency room: need for intubation; seizures; unresponsiveness to verbal stimuli; arterial carbon dioxide pressure (tension) greater than or equal to 45 mm Hg; any rhythm except sinus; second- or third-degree atrioventricular block; QRS greater than or equal to 0.12 s; or systolic pressure less than 80 mm Hg. Of 151 low-risk patients, none developed a high-risk condition after admission, and none required an intensive care intervention. The use of these predictive criteria in our patient population would have eliminated over half the intensive care days without compromising quality of care.