A 1-year prospective study of 12 hospitals, and approximately 1 million people, was carried out to predict the effectiveness of prehospital advanced life support (ALS) for major trauma in Northern Ireland. Inclusion criteria were an Injury Severity Score (ISS) > 15 and reaching hospital alive. Two hundred and thirty-nine patients had mean prehospital times of 24 and 35 min for urban and rural hospitals, respectively. Most patients (75 per cent, N = 179) were within 10 minutes of a hospital. Of the other patients (25 per cent, N = 60), only 1/2 would have benefitted from prehospital ALS. Fifteen patients aspirated (for a mean time of 7 minutes) before ambulance arrival and eventually died. Seventy per cent of patients who died and who either aspirated or were apnoeic had severe primary brain injuries; the other 30 per cent were considered unsalvageable by both TRISS and peer review. ALS for major trauma will be appropriate for less than 50 patients with ISS > 15 per annum in Northern Ireland. Skill maintenance will be difficult for paramedics.