An analysis of the completed Major Trauma Outcome Study (MTOS) data set was undertaken to compare the incidence, mortality, morbidity, and injury severity of patients with head injuries (HI) with those of patients with extracranial injuries (ECI). The MTOS was completed recently after data from 174,160 patients submitted from 165 trauma centers from 1982 through 1989 were collated and validated. Data were analyzed with regard to the effect of injury causation for vehicular-related, nonvehicular-related, and penetrating injuries for patients with HI, ECI, or both. Detailed analyses of relationships between AIS-85 and Glasgow Coma Scale score from the entire data base, and between discharge status, functional independence measures (FIM scores), and severity of HI and ECI in a subset of 70,000 surviving patients were performed. Vehicular-related injuries (49.7%) were divided into those to vehicle occupants (36.4%), pedestrians (7.2%), and motorcyclists (6.0%). Nonvehicular-related blunt injuries included falls (18.4%) and assaults (13.2%) and penetrating injuries consisted of gunshots (8.7%), stabbings (8.0%), and other penetrations (1.8%). There were 59,713 patients with HI (34%) and 114,447 with no head injuries (NHI) (66%). Vehicular causes produced more HI (66.6%) than all other causes, despite the preponderance of nonvehicular-related HI in the overall series (50.3%). The overall MTOS mortality rate was 8.3%, but was three times higher in the HI group (14.5%) than in the NHI patients (5.1%). Injury severity measured by AIS-85 had, as expected, a profound influence on mortality of both HI and NHI groups. A similar high correlation was found between Glasgow Coma Scale score and mortality for head injured patients.(ABSTRACT TRUNCATED AT 250 WORDS)