BACKGROUND: The optimal composition of lipid emulsions in parenteral nutrition (PN) for premature infants remains controversial. This study examined the effects of a combination of soybean oil-based (SoyLE) and fish oil-based (FishLE) lipid emulsions compared to FishLE as monotherapy on the lipid and fatty acid profiles and clinical outcomes of premature infants requiring prolonged PN. METHODS: 42 premature infants received FishLE+SoyLE or FishLE. Serum concentrations of lipoproteins and 29 fatty acids (FA) were measured at baseline, 4, and 8 weeks of PN and growth and neurodevelopmental outcomes were measured at 3, 6, 12, 18, and 24 months of life. RESULTS: Lipid profiles were similar between groups. Plasma concentrations of ω-6 fatty acids tended to decrease over time in both groups. Concentrations of most ω-3 fatty acids, in particular docosapentaenoic acid, eicosapentaenoic acid, and docosahexaenoic acid, were significantly increased over time in the FishLE+SoyLE group whereas they did not change in the FishLE alone group. However, serum concentrations of almost all fatty acids were similar between groups at the end of the study period. No differences in growth parameters including weight, height, fronto-occipital circumference (FOC), and body mass index (BMI) were observed up to two years of age. Similarly, there were no differences in neurodevelopmental test scores at 6, 12, 18, and 24 months of age. CONCLUSIONS: No substantial differences in lipid profiles and short clinical outcomes were found in infants exposed to FishLE+SoyLE when compared to FishLE.