Subdural haematoma is one of the commonest features of the battered child syndrome, yet by no means all the patients so affected have external marks of injury on the head. This suggests that in some cases repeated acceleration/deceleration rather than direct violence is the cause of the haemorrhage, the infant having been shaken rather than struck by its parent. Such an hypothesis might also explain the remarkable frequency of the finding of subdural haemorrhage in battered children as compared with its incidence in head injuries of other origin, and the fact that it is so often bilateral.