Belgium is known to have a lesser low birthweight rate and a lower infant mortality rate than the United States. We used previously unpublished data to show that beneath this comparison lies a more complicated picture. Singleton live birth certificates for 1986-87 were analysed. Despite a lower mean birthweight in Belgium (3360 g) than in the United States (3420 g), Belgium had fewer (4.9%) low birthweight infants than the US (5.9%) because of fewer preterm births (4.4 vs. 9.3%). Consistent with the excess of preterm births in the US, the residual distribution of birthweight was smaller in Belgium (2.2% vs. 3.1%). Whereas neonatal mortality was 4.8/1000 in Belgium and 5.6/1000 in the US, birthweight-specific neonatal mortality was higher in Belgium. The challenge for Belgium is to improve the survival of newborns regardless of their birthweight. In the US, the task is to eliminate the excess of small preterm infants.