The Rapid Acute Physiology Score (RAPS) was developed and tested for use as a severity scale in critical care transports. RAPS is an abbreviated version of the Acute Physiology and Chronic Health Evaluation (APACHE-II) using only parameters routinely available on all transported patients (i.e. pulse, blood pressure, respiratory rate, and Glasgow Coma Scale). RAPS has a range from 0 (normal) to 16. Two hundred eighty-three patients were transported by helicopter; 62 died. Pretransport RAPS was available on 282 of 283 patients (mean, 3.85; median, 3). Because of death, discharge, or transfer, 227 complete APACHE-II scores using least physiologic values for the first 24 hours after transfer were collected (mean, 14.98; median, 13). Stepwise logistic regression showed that when all APACHE-II and RAPS values were available, the best single predictor of mortality was worst value APACHE-II (X2(1) = 57.09, P less than .01). When pretransport RAPS was considered as a single explanatory variable, it too had significant predictive power for mortality (X2(1) = 92.53, P less than .01). Correlation analysis comparing RAPS with APACHE-II values at similar points in time revealed a significant relationship in all cases, with the highest correlation between RAPS worst values and APACHE-II worst values (r = .8472, P less than .01). It was concluded that RAPS can be applied usefully in complement with APACHE-II and may have limited utility when used alone.