The effect of admission to hospital after a minor head injury on the incidence and duration of post-concussional symptoms was investigated. A total of 114 adults with a minor head injury were randomly allocated to admission for 24 h or to discharge from the accident department. Follow-up was by postal questionnaire. This revealed that 90 per cent of patients suffered symptoms lasting an average of 2 weeks. The patients who were discharged had symptoms that lasted a shorter time. Admission to hospital does not reduce the incidence and severity of symptoms following minor head injuries in adults.