This systematic review demonstrates that, in patients sustaining minor head injury with a history of loss of consciousness or amnesia, the proportion who subsequently have positive CT scans is not negligible. Published clinical prediction rules for selecting patients for subsequent CT examination are associated with a trade-off between sensitivity and specificity; therefore, a prediction rule with high sensitivity is expected to have relatively low specificity. Separate evaluation of the literature is required to determine the significance of positive and negative CT scans with respect to patient outcome.