In the United States, annual influenza vaccine is now recommended for all children 6 months through 18 years of age. This 2-year observational study of US outpatient pediatricians' offices captured office demographics and characteristics, recorded all influenza vaccinations administered and vaccination-related activities during the influenza season, and correlated office characteristics and activities associated with increased vaccine uptake. Offices generally offered the influenza vaccine from September through February and March; however, approximately 80% of vaccinations occurred in October through December. In 2008-2009 compared with 2007-2008, offices administered the vaccine earlier and later into the season. Estimated in-office rates of first-dose administration, 2-dose compliance, and use of the intranasal vaccine also increased. Qualitative analyses suggest that increased first-dose administration and 2-dose compliance rates are associated with smaller office size and a greater duration of vaccine availability, respectively, during both seasons.