We conducted a meta-analysis of 13 randomised clinical trials evaluating the efficacy of influenza vaccine in healthy children. Against culture-confirmed influenza the overall efficacy was 74% (95% confidence interval, CI, 57%-84%), 65% for inactivated and 80% for live-attenuated vaccine. Corresponding figures were 59% (95% CI 43%-71%), 63% and 54% for serologically-confirmed influenza, and 33% (95% CI 29%-36%), 33% and 34% for clinical illness. Influenza vaccine is effective in preventing laboratory-confirmed and clinical influenza in healthy children, with no clear difference between inactivated and live-attenuated vaccine. Data on infants and younger children were too scanty to allow separate assessment.