Following a long period of fairly steady increase, the U.S. preterm birth rate declined for the second straight year in 2008 to 12.3 percent, from 12.8 percent in 2006. This marks the first 2-year decline in the preterm birth rate in nearly three decades. Preterm birth rates declined from 2006 to 2008 for mothers of all age groups under age 40, for the three largest race and Hispanic origin groups and for most U.S. states. The percentage of preterm births was down for all types of deliveries from 2006 to 2008, for cesareans and for induced and noninduced vaginal deliveries.