Metropolitan Houston with a population of four million has the nation's poorest freeway system. Its two Level I trauma centers are adjacent within a centrally located freeway loop, therefore the city is ideally suited for a trauma scene helicopter transport service. During 1981 there were 577 flights to the scene of injury (blunt, 466; penetrating, 111). Flights were requested by 60 agencies (EMS, law enforcement, etc.). All flights were manned by a surgical resident and flight nurse. The flight distances ranged from 2 to 57 miles (average, 14.4). Three hundred six flights (53%) were within the city, including 59 (10.2%) within the freeway loop. In approximately one half of the flights, the initial responding EMS unit was a paramedic unit. The average time at the scene was 28 minutes. The overall mortality for trauma scene flights was 35.7% (206/577). Eighty-nine patients (15.1%) died at the scene and were not transported (initial median scene Trauma Score, 2). The mortality among transported patients was 24.0% (117/488). Twenty-nine patients died during attempted emergency-center resuscitation (initial median scene Trauma Score, 5). Eight-eight patients died after hospital admission (initial median scene Trauma Score, 10). Only 27 patients (5.5%) did not require hospitalization. Scene treatment (intubation, hyperventilation and, when appropriate, mannitol administration) was routinely initiated for patients with severe head injuries. Two hundred seventy-nine patients required cardiopulmonary resuscitation, tracheal intubation, chest-tube placement, or other invasive procedures. Based upon these resuscitative efforts and invasive procedures, a physician in attendance was deemed medically desirable for one half of the flights.(ABSTRACT TRUNCATED AT 250 WORDS)