Clinicians'estimates of expected impairment resulting from 7,502 single injuries to head, abdomen and lower limb have been compared with corresponding Injury Impairment Scale scores. 33.4% were expected to make a full recovery, 62.4% to have a temporary impairment and 4.2% a permanent impairment. IIS scores were 0 (40.1%), 1 (46.9%), 2 (8.5%) >2 (4.5%). There were strong correlations between physicians' estimates of impairment severity and IIS globally, for specific injuries and for age 25-40. These results do not validate the IIS but do suggest that it will have credibility with practicing trauma clinicians.