BACKGROUND: The incidence of awareness has been reported to be higher in children than in adults. Accurately assessing awareness in children is difficult, and the lack of a specific measure of awareness makes it difficult to determine exactly how many and why children are aware. The aim of this study was to determine the incidence and timing of awareness in children by using auditory stimuli applied during anesthesia. METHODS: Three easily identified animal noises were played repeatedly through headphones during three specific phases of anesthesia in 539 children aged 5-12 yr. Children were not told that this would happen. Awareness was determined with a structured interview on days 1 and 3 after the anesthetic. All positive responses were sent to four adjudicators for assessment, and awareness was defined as having occurred if all adjudicators agreed that the child was aware. RESULTS: Five hundred children were interviewed at least once after the anesthetic. Thirty-five reports were sent to the adjudicators, and one child was classified as aware. This child was deemed to be aware even though he did not report hearing an animal. CONCLUSIONS: The incidence of awareness in this study is less than reported previously.