Patients with phenylketonuria (PKU) have a poor LC-PUFA status and require supplementation. The objective of this study was to evaluate the LC-PUFA status of PKU patients supplemented with fish oil or the fatty acid supplement KeyOmega. Plasma and erythrocyte docosahexaenoic acid (DHA) and arachidonic acid (AA) levels were determined in 54 patients (1-18.5years of age) with confirmed PKU. The influence of supplementation with fish oil versus KeyOmega, a powdered blend of DHA and AA, on LC-PUFA status was investigated and compared to the status in samples obtained from unsupplemented patients. Differential effects on LC-PUFA status were observed upon suppletion with fish oil versus KeyOmega. Whereas supplementation with fish oil increased the level of DHA, the AA concentration did not increase to normal values in these patients. In contrast, both DHA and AA levels increased and reached reference values upon supplementation with KeyOmega. In conclusion: these results indicate that KeyOmega offers additional benefit over fish oil since both AA and DHA status are normalized in PKU patients supplemented with KeyOmega.