The U.S. infant mortality rate was 6.78 infant deaths per 1000 live births in 2004 compared with 6.84 in 2003. Infant mortality rates ranged from 4.67 per 1,000 live births for Asian and Pacific Islander mothers to 13.60 for non-Hispanic black mothers. Among Hispanics, rates ranged from 4.55 for Cuban mothers to 7.82 for Puerto Rican mothers. Infant mortality rates were higher for those infants whose mothers were born in the 50 states and the District of Columbia, were unmarried, or were born in multiple births. Infant mortality was also higher for male infants and infants born preterm or at low birthweight. The neonatal mortality rate declined from 4.63 in 2003 to 4.52 in 2004 while the postneonatal mortality rate was essentially unchanged. Infants born at the lowest gestational ages and birthweights have a large impact on overall U.S. infant mortality. More than one-half (55 percent) of all infant deaths in the United States in 2004 occurred to the 2 percent of infants born at less than 32 weeks of gestation. Still, infant mortality rates for late preterm (34-36 weeks of gestation) infants were three times those for term (37-41 week) infants. The three leading causes of infant death-Congenital malformations, low birthweight, and SIDS-taken together accounted for 45 percent all infant deaths. Results from a new analysis of preterm-related causes of death show that 36.5 percent of infant deaths in 2004 were due to preterm-related causes. The preterm-related infant mortality rate for non-Hispanic black mothers was 3.5 times higher, and the rate for Puerto Rican mothers was 75 percent higher than for non-Hispanic white mothers.