When planning a trauma service it is important to estimate the number of injured patients who will attend a hospital other than the designated trauma centre. Up to a third of patients in one study went to the wrong hospital.' This happens because paramediCs make triage errors and take patients to the wrong hospitaF and (we hypothesise) because some patients make their own way to hospital. Because a trauma service may be established in Northern Ireland we tried to estimate the numbers of injured patients likely to take themselves to the wrong hospital.