A multi-institutional study was undertaken to define the predictive power for mortality of the Rapid Acute Physiology Score (RAPS) in a large and diverse group of transported patients. RAPS is a truncated version of the Acute Physiology and Chronic Health Evaluation (APACHE II) score that uses definitions and weighting consistent with APACHE II, but is modified to provide a consistent score just before transport, just after transport, and to use the most deranged (worst) physiologic values during the initial 4 h after arrival at the receiving hospital. During an 8-month period, 1,927 patients transported by six helicopter emergency medical service programs were studied. Over 97% (1,881) of the patients had RAPS obtained before and after transport to the receiving hospital and 92.6% (1,785) had APACHE II scoring completed after hospital admission. Receiver operating curves demonstrate similar predictive power for RAPS and APACHE II (both based on the most deranged physiologic values during the initial 24 h after admission). Before- and after-transport RAPS were also highly predictive of mortality. RAPS appears to be a reliable and highly predictive measure of patient severity/physiologic stability before and after transport to critical care.