Increasing workloads in our radiology department prompted a study of casualty officers' use of x ray examinations, of which there were 5463 in the period. While casualty officers were in post referrals for x ray examination did not become more selective, but skills in interpreting films improved. Overall, 4.9% of trauma radiographs were misinterpreted, but this fell from 7.1% to 2.9% during tenure of post. One in four errors was clinically important. Clinical guidelines for selective radiography produced a significant and sustained reduction in the number of x ray examinations requested by the department. Analysis of one common injury indicated that the quality of patient care was not adversely affected. The number of x ray examinations carried out in the accident and emergency department can be reduced by using guidelines, and this does not compromise the quality of patient care. Appreciable savings may be made in patients' waiting times and radiodiagnostic expenditure.