The possibility that early nutrition has long term consequences in man has been much debated. There have been limited opportunities to perform formal randomised studies on the effect of early nutrition in man and many studies have been flawed by problems with study design. Infants born preterm are a special group. At the start of this study in 1982 evidence on which to base choice of diet was inconsistent and related only to short term outcome, and diets available for such babies differed greatly in nutrient content. In this group it was both ethical and practical to conduct a formal, randomised trial of early diet and outcome and the results were clearly for management decisions. A long term prospective outcome study was undertaken on 926 preterm infants randomly assigned to the diet received in the neonatal period. Surviving children have been followed at 9 months, 18 months, and now 7 1/2-8 years of age. The findings suggest that children fed a nutrient supplemented preterm formula perform better than those fed a standard formula milk, and also that human milk may contain factors which promote brain growth or development. Outcome data from the randomised trials show that a very brief period of dietary manipulation (on average for the first 4 weeks of life) influences later development.