OBJECTIVE: To examine the predictive value of a crack noise or sensation in the history of injury in the diagnosis of ankle fracture. METHODS: A short questionnaire was filled in on 464 patients with isolated ankle injuries attending the accident and emergency department in a three month period from July to September. These patients were seen in the usual way in the department and the need for x ray assessed according to clinical judgement and existing departmental guidelines. Cases which subsequently proved to be other than ankle injuries, for example, fractured calcaneus, were excluded from the study. RESULTS: A positive history of hearing or feeling a crack did not indicate the need for an x ray or increase the possibility of a fracture; indeed the history of a crack made the presence of a fracture less likely. The clinical diagnosis of absence of fracture without radiological examination may require careful explanation to the patient. CONCLUSIONS: Hearing a crack in the ankle does not suggest a fracture.