The case is described of a child in whom unilateral neurological signs were observed during anaesthesia. These signs had not previously been elicited when the child had been examined whilst conscious. On further examination when consciousness had been regained the signs were only apparent to a limited extent but became more apparent over the following two months. The underlying pathological lesion was later discovered to be a cerebral tumour. A series of children were then examined during anaesthesia and after recovery. The significance of the findings is discussed.