KEY FINDINGS: Data from the Linked Birth/Infant Death Data Set and Preliminary Mortality Data File, National Vital Statistics System. The U.S. infant mortality rate did not decline from 2000 to 2005. Data from the preliminary mortality file suggest a 2% decline in the infant mortality rate from 2005 to 2006. The U.S. infant mortality rate is higher than those in most other developed countries, and the gap between the U.S. infant mortality rate and the rates for the countries with the lowest infant mortality appears to be widening. The infant mortality rate for non-Hispanic black women was 2.4 times the rate for non-Hispanic white women. Rates were also elevated for Puerto Rican and American Indian or Alaska Native women. Increases in preterm birth and preterm-related infant mortality account for much of the lack of decline in the United States' infant mortality rate from 2000 to 2005. Infant mortality is one of the most important indicators of the health of a nation, as it is associated with a variety of factors such as maternal health, quality and access to medical care, socioeconomic conditions, and public health practices. The U.S. infant mortality rate generally declined throughout the 20th century. In 1900, the U.S. infant mortality rate was approximately 100 infant deaths per 1,000 live births, while in 2000, the rate was 6.89 infant deaths per 1,000 live births. However, the U.S. infant mortality rate did not decline significantly from 2000 to 2005, which has generated concern among researchers and policy makers.