Most studies evaluating the growth of preterm infants use the socalled intrauterine growth curve and reference fetus as standards. These curves might not be the optimal standards, however, for several reasons. The curves were constructed from small numbers of infants with uncertainty about gestational age, reasons for preterm birth, and, for body-composition data, the reasons for the death of the infant. Second, preterm infants after birth are not comparable with fetuses, being in a completely different environment and receiving a completely different nutrition. For instance, a higher percentage of body fat in preterm infants might well be an adequate adaptation to their environment. To get preterm infants to adhere to their supposed growth curve percentile, catch-up growth is needed. Recent studies indicate that catch-up growth might be advantageous for brain development. It might at the same time increase the incidence of cardiovascular disease in later life. The use of intrauterine growth curves to evaluate postnatal growth needs a critical reevaluation. Am J Clin Nutr 2007;85(suppl):608S-13S.