BACKGROUND This study aimed to examine the validity of using Maryland hospital discharge data to characterize injuries sustained by trauma patients. METHODS Maryland hospital discharge and Maryland trauma registry data for 1999 were merged, and the extent of agreement regarding the presence and severity of injuries sustained was evaluated. RESULTS The mean Injury Severity Score was 8.4 according to the Maryland hospital discharge data and 10 according to the Maryland trauma registry data (p < 0.0001). The Maryland hospital discharge data identified 95% or more of all moderate to severe injuries (Abbreviated Injury Score, > or =2) for all body regions except the head. There was substantial agreement between the two data sets for mechanism of injury (weighted kappa, 0.62), the number of preexisting conditions present (weighted kappa, 0.45) and final disposition (weighted kappa, 0.78). CONCLUSIONS The Maryland hospital discharge data are a valid source for documenting the nature and severity of injuries sustained by trauma patients, except for those with a relatively minor head injury.