Improvement in trauma management requires a better understanding of the effect of a patient's preinjury health status on outcome. Specific historical findings and laboratory criteria were used to define pre-existing disease (PED) states and determine if they were independent predictors of fate in trauma victims. Of 7,798 adult patients admitted to a level I trauma center from July 1986 through June 1990, 16.0% (1,246) had greater than or equal to 1 PED. The PED+ and PED- patients had no significant difference in Injury Severity Scores (ISSs) (15.7 versus 15.6) and admission Glasgow Coma Scale (GCS) scores (13.9 versus 13.8). The PED+ patients were older (49.2 versus 30.6 years) (p less than 0.001) and had a higher mortality rate (9.2% versus 3.2%) (p less than 0.001) than PED- patients. Mortality rates were also elevated for patients with greater than or equal to 2 PEDs (18%) and for those with renal disease (38%), malignancy (20%), and cardiac disease (18%) (p less than 0.001) compared with PED- patients. Controlling for age and ISS, there was an association between PED and mortality (Mantel-Haenszel p less than 0.03). Multivariate regression showed that PED is an independent predictor of mortality (R2 = 0.1918; p less than 0.0001). The greatest increases in mortality were found among patients less than 55 years and with ISS less than 20. Changes in prehospital triage criteria and outcome scoring are needed. Improvements in the management of trauma victims with chronic disease may decrease their mortality rate.