Measurement of newborn babies is widely regarded as being too inaccurate to justify its regular practice. It is common for infants to be weighed at birth and for no other measurements to be made. Although such assumptions are superficially correct, it is possible to train people to perform accurate measurements and for improved performance to be sustained. Accurate sequential measurements are possible and provide more information than single measurements. Detailed measurements show that postnatal growth may change rapidly and dramatically, particularly in preterm infants. Postnatal growth impairment is common in such infants and may be sustained. Limited evidence suggests that there may be a significant reduction in final stature. Preliminary data also suggest that many preterm infants may also show evidence of alterations in biochemical and physiological variables consistent with early programming and the potential for altered disease susceptibility in adult life.