Invasive pneumococcal disease (IPD), caused by Streptococcus pneumoniae (pneumococcus), remains a leading cause of serious illness in children and adults worldwide. After routine infant immunization with a 7-valent pneumococcal conjugate vaccine (PCV7) began in 2000, IPD among children aged <5 years in the United States decreased by 76%; however, IPD from non-PCV7 serotypes, particularly 19A, has increased. In February 2010, the Advisory Committee on Immunization Practices (ACIP) issued recommendations for use of a newly licensed 13-valent pneumococcal conjugate vaccine (PCV13). PCV13 contains the seven serotypes in PCV7 (4, 6B, 9V, 14, 18C, 19F, and 23F) and six additional serotypes (1, 3, 5, 6A, 7F, and 19A). To characterize the potentially vaccine-preventable IPD burden among children aged <5 years in the United States, CDC and investigators analyzed 2007 data from Active Bacterial Core surveillance (ABCs). This report summarizes the results of that analysis, which found that among 427 IPD cases with known serotype in children aged <5 years, 274 (64%) were caused by serotypes contained in PCV13. In 2007, an estimated 4,600 cases of IPD occurred in children in this age group in the United States, including approximately 2,900 cases caused by serotypes covered in PCV13 (versus 70 cases caused by PCV7 serotypes). PCV13 use has the potential to further reduce IPD in the United States. Post-licensure monitoring will help characterize the effectiveness of PCV13 in different populations and track the potential changes in disease burden caused by non-PCV13 serotypes.