The long-chain polyunsaturated fatty acids (LCPUFA) docosahexaenoic acid (DHA; C22:6n-3) and arachidonic acid (ARA; C20:4n-6) have important physiological implications and are required for optimal somatic growth and brain development, particularly in the early years of life. The objective of this study was to determine if children with PKU have lower plasma EFA concentrations than healthy, sex and age-matched control subjects.