There has been growing interest in the role of n-3 long-chain polyunsaturated fatty acids (LC-PUFA) in the modulation of the immune response during early childhood and whether this may translate to a reduction in childhood allergic disease. Several randomized controlled trials of n-3 LC-PUFA supplementation have been reported, largely involving children who are at high hereditary risk of developing allergies. These studies relatively consistently indicate that supplementation during pregnancy results in fewer children with atopic eczema in early childhood. On the other hand, supplementation studies confined exclusively to the postnatal period have demonstrated mixed results with one trial showing no effect and the other suggesting a transient effect on symptoms of respiratory disease. In summary, supplementation with n-3 LC-PUFA during the perinatal period and before allergic response is established may be a useful strategy to prevent early childhood allergic disease in children at high hereditary risk. Further work is needed to establish the optimal period of supplementation and whether longer term benefits exist.