We reviewed the clinical characteristics and resource utilization of 391 medical (M) and 315 surgical (S) ICU patients. In general, MICU patients had more physiologic derangement, as determined by the admission, maximal, and average acute physiology scores (APS). SICU patients had more frequent therapeutic interventions as measured by admission, maximal, and average therapeutic intervention scoring system values. Notably, 40% of MICU and 30% of SICU patients never received any active interventions and were admitted strictly for monitoring purposes. Patients on admission with APS less than or equal to 10 had markedly shorter ICU stays, with almost 50% less treatment than patients with APS over 10. Fifty-six percent of patients with APS less than or equal to 10 did not require any active intervention. In contrast, 83% of patients with APS greater than 10 had considerable intensive interventions. These patients required mechanical ventilation, invasive monitoring, and vasoactive drugs more than twice as often as patients with lower APS scores. Consideration should be given, therefore, to the organization of ICUs according to the patient's severity of illness.