Purpose : We conducted a prospective comparative clinical study to determine the field efficacy of the 2010-2011 influenza vaccines [Influenza virus strains; A/California/7/2009 (H1N1), A/Perth/16/2009 (H3N2), B/Brisbane/60/2008] in healthy Korean children under 18 years of age. Methods : In this study, we enrolled subjects aged between 6 months and 18 years and divided them into 2 study groups: a group who received the influenza vaccines (407 subjects), and a control group who did not receive the influenza vaccines (230 subjects). Ours was a multicenter study that involved 7 hospitals, including the Korea Cancer Center Hospital. The study was conducted between September 2010 and February 2011. We collected nasal wash or throat swab samples from subjects who presented with acute febrile respiratory or influenza-like illnesses at the hospital. We used PCR to confirm the presence of the influenza virus in the respiratory samples and characterize the virus type. Results : In this study, we collected 22 respiratory samples from the influenza-vaccinated group and found 3 cases of influenza virus infection. Similarly, we collected 21 samples from the control group and found 12 cases of influenza virus infection among 10 subjects during the study period. We determined the field efficacy of the 2010-2011 seasonal influenza vaccines to be 83.2% in healthy Korean children and adolescents. Conclusion : In this study, we determined the field efficacy of the 2010-2011 seasonal influenza vaccines in healthy Korean children and adolescents. We found that the field efficacy of 2010-2011 seasonal influenza vaccines was adequate.