The body composition of 70 appropriate for gestational age newborn infants whose gestational age ranged from 32 to 41 weeks was determined by dual-energy X-ray absorptiometry during the first 48 h of life. The evolution of the bone mineral content, fat and lean mass was well correlated with gestational age (r = 0.66, r = 0.66 and r = 0.82, respectively) but even more closely with birthweight (r = 0.85, r = 0.91 and r = 0.97, respectively). The body composition of 20 symmetric small for gestational age infants (mean gestational age +/- SD = 38.1 +/- 1.2 weeks; mean birthweight +/- SD = 2117 +/- 183 g) was also studied. The total body fat, the lean mass and the bone mineral content of small for gestational age infants were decreased significantly in comparison with those of appropriate for gestational age infants with the same gestational age (p < or = 0.05, p < or = 0.0001 and p < or = 0.05) but was not significantly different from those observed in appropriate for gestational age infants of the same birthweight.