Gestational age and neonatal anthropometric parameters are currently used to evaluate fetal growth and are predictive factors of perinatal and postnatal morbidity and mortality. We performed a retrospective analysis of neonatal anthropometric parameters (weight, vertex-heel length and head circumference) in 1,470 live preterm neonates born between 1997 and 2002 and a prospective analysis of the same parameters in 1,786 live newborns of both sexes born in 2001 and 2002, products of single 37-42 week uncomplicated pregnancies in healthy Spanish Caucasian mothers. A progressive increase in these parameters with gestational age and sexual dimorphism were observed from the 30th week of gestational age onwards, with statistically-significant differences (p<0.05) at 38-42 weeks of gestational age. An increase in weight and length values in relation to previous Spanish studies was also documented in preterm newborns. It is estimated that 10-15% of children born small for gestational age (SGA) do not experience catch-up growth by the age of 3 years and may have short stature in adulthood. Preliminary data of a cross-sectional study on spontaneous growth in boys and girls born SGA without postnatal catch-up growth show that their +2 SD values of height are similar to -2 SD values of our normal control population of children born with adequate weight and length for gestational age (AGE). However, weight +2 SD values are similar to mean values of control children born AGE. In summary, our data show sexual dimorphism in neonatal anthropometric growth parameters and that these parameters change with time and may be updated. In addition children born SGA without postnatal catch-up are shorter and have higher weight than age-, height- and sex-matched controls born AGE.