A dietary supply of docosahexaenoic acid (DHA, 22:6n-3) during the perinatal period is postulated to be important for the neurodevelopmental outcome of children. This paper reviews the results of two large scale intervention trials in which equivalent dietary doses of DHA were assessed. One trial assessed the ex utero effect of DHA supplementation for preterm infants born <33 weeks' gestation while the other trial assessed the in utero effect of DHA supplementation during the second half of pregnancy. Ex utero DHA supplementation, which aimed to achieve the level of DHA accumulation that would occur in the womb, appeared more effective in improving the neurodevelopmental outcome of preterm children rather than in utero DHA supplementation of unborn infants. Significant treatment by sex and treatment by birth weight interactions were noted indicating that boys and girls respond differently to DHA supplementation and that birth weight may also be important in predicating the DHA responsiveness.