OBJECTIVE: To examine the use made of 24 hour access to computed tomography from an accident and emergency (A&E) department and to assess whether clear benefits for patients could be identified by having such a service. METHODS: Retrospective review of 176 cases where computed tomography was ordered by A&E staff of a large teaching hospital over a one year period. RESULTS: 53% of scans were done "out of hours"; 97% of scans performed (171/176) were studies of the brain. Three examinations were of the cervical spine and two were of the chest. 54% of head scans (93/171) were performed for either confirmed or suspected trauma with 46% (78/171) done for medical indications. Only 16% (11/71) of patients who had a head scan for acute trauma required transfer to the regional neurosurgical unit after consultation. Computed tomography was 100% sensitive in the diagnosis of sub-arachnoid haemorrhage. In cases where computed tomography was performed for coma of undetermined origin the pathology causing coma was identified on computed tomography in 50% of cases. CONCLUSIONS: Computed tomography facilities allow comprehensive initial evaluation of the head injured patient and minimise hazardous and expensive transfer of these seriously ill patients. Experience shows that it is a vital tool in the initial differential diagnosis of the comatose patient and therefore must be available for use by senior and middle grade A&E staff on a 24 hour basis.