Breastfeeding is associated with decreased risk for many early-life diseases and conditions, including otitis media, respiratory tract infections, atopic dermatitis, gastroenteritis, type 2 diabetes, sudden infant death syndrome, and obesity. Breastfeeding also is associated with health benefits to women, including decreased risk for type 2 diabetes, ovarian cancer, and breast cancer. Exclusive breastfeeding is defined as an infant receiving only breast milk and no other liquids or solids except for drops or syrups consisting of vitamins, minerals, or medicines. In 2007, Healthy People 2010 (HP2010) objectives for breastfeeding initiation and duration were updated to include two new objectives on exclusive breastfeeding (i.e., to increase the proportion of mothers who exclusively breastfeed their infants through age 3 months to 60% and through age 6 months to 25% [objectives 16-19d and 16-19e]). To monitor progress toward achieving HP2010 breastfeeding objectives, CDC analyzed data from the National Immunization Survey (NIS). This report describes the results of that analysis, which indicated that rates for breastfeeding initiation and duration increased among infants born during 2000-2004. Rates for exclusive breastfeeding through ages 3 months and 6 months among infants born in 2004 were 30.5% and 11.3%, respectively, below targets set by HP2010. Rates of exclusive breastfeeding were significantly lower among black infants (compared with white infants) and infants born to unmarried mothers (compared with married mothers). Additionally, older age, urban residence, higher education, and higher income of mothers all were positively associated with exclusive breastfeeding. Further research is needed to identify successful programs and policies to support exclusive breastfeeding, especially among subgroups with the lowest rates.