A retrospective review of 1900 road accident victims attending the emergency departments of two Melbourne hospitals was undertaken to identify Injury Severity Score levels which could distinguish between minor, moderate, severe and critical injury. Injuries scoring ISS 6 or below were designated 'minor' because they were associated with a low risk of requiring admission to hospital. Case notes of patients scoring above ISS 6 were then reviewed by a panel of clinicians, who independently rated each patient's overall injury severity as moderate, severe or critical according to what was recorded in the notes and their 'clinical' judgement. ISS values were compared with clinicians' ratings. Measures of each clinician's individual rating consistency, and correlation between pairs of clinicians with respect to inter-rater consistency, were made. By combining data from both hospitals it emerged that 'moderate' injury corresponded to ISS 8-13, 'severe' to ISS 14-20 and 'critical' to ISS 21 and above. These ISS breakpoints will be useful in selecting groups of injured patients for future trauma audit studies.