The objective of this study was to investigate how many patients with minor head injury would have required computerised tomography (CT) imaging if they were to be managed according to the National Institute of Clinical Excellence (NICE) guidelines (June 2003) and the difference in workload for patients presenting out of hours at Calderdale Royal Hospital, Halifax. The study was a retrospective cohort analysis of patient's notes presenting with head injury at Calderdale Royal Hospital, Halifax. The data set comprised case notes of 844 patients with head injuries, 400 adults and 444 children attending the Accident and Emergency department from January to June 2003. The case notes were evaluated according to the NICE guidelines for the indications for CT imaging for the time that they presented to the Accident and Emergency department, and how many of them actually underwent CT imaging. The number of patients who required CT imaging and how many of them presented out of hours (between 17:00 and 21:00 hours on weekdays and at any time on weekends). Ten patients underwent CT imaging for minor head injuries from January to June 2003. Eighty-eight patients required CT imaging if they were to be managed according to the NICE guidelines. Sixty-three per cent of these patients presented out of hours when a radiologist was not available in the hospital. Adhering to the NICE guidelines would significantly increase the number of patients requiring CT imaging. A significant proportion of these patients would present out of hours.