OBJECTIVE: The purpose of this study was to monitor the clinical and microbiologic features of invasive infections caused by Streptococcus pneumoniae among children before and after the introduction of the 7-valent pneumococcal conjugate vaccine (PCV7). DESIGN: We conducted a 15-year prospective surveillance study of all invasive pneumococcal infections in children. The sample included infants and children at 8 children's hospitals in the United States with culture-proven invasive S pneumoniae infections. RESULTS: Since the implementation of routine PCV7 immunization in 2000, invasive infections have decreased yearly from 2001 through 2004, to a nadir of 151 infections; the rate then increased from 2005 through 2008. Compared with the pre-PCV7 era, a greater proportion of children with invasive pneumococcal infection had an underlying condition in the post-PCV7 period. Compared with the total number of annual admissions, the number of 19A isolates increased significantly from 2001 to 2008 (P < .00001). In 2007 and 2008, only 16 isolates (4%) were vaccine serotypes; 19A accounted for 46% (168 of 369) of the non-PCV7 serotypes. Thirty percent of the 19A isolates were multidrug resistant. Serotypes 1, 3, and 7F accounted for 22% of the non-PCV7 serotypes. Among children with invasive pneumococcal infections, the likelihood of a 19A serotype increased with the number of preceding PCV7 doses. CONCLUSIONS: Since 2005, the number of invasive pneumococcal infections in children has increased at 8 children's hospitals, primarily as a result of serotype 19A isolates, one third of which were resistant to multiple antibiotics in 2007 and 2008. Continued surveillance is necessary to detect emerging serotypes after the planned introduction of 13-valent or other pneumococcal vaccines.