OBJECTIVE: The objective of this study was to assess the safety of routine trivalent influenza vaccine (TIV) administration among healthy children 6 through 23 months of age, after the Advisory Committee on Immunization Practices recommendation. METHODS: The study was a retrospective case-control study of children receiving TIV in the first 2 seasons after the Advisory Committee on Immunization Practices recommendation. We assessed outcomes in the 42 days after vaccination in a population of 13,383 children. Each case subject was matched, according to age and gender, with 3 control subjects. Hazard ratios were calculated with conditional logistic regression analysis. RESULTS: We found no statistically significantly elevated hazard ratios for the first TIV dose. An elevated risk of pharyngitis was found for children receiving a second TIV dose. No elevated risk of seizure was found. CONCLUSION: These results, for a population of healthy children, showed no medically significant adverse events related to TIV among children 6 to 23 months of age.