We correlated arachidonic acid (AA) and docosahexaenoic acid (DHA) status with anthropometric measures and growth rates in a group of low birth weight infants (≤2500 g; gestational ages 30–41 weeks; n = 143). AA and DHA status were measured in erythrocytes (RBC) and plasma cholesterol esters (CE) during days 10 to 42. Infants received preterm formula without long-chain polyunsaturated fatty acids (LCP; n = 81), with LCP (n = 29) or maternal milk (n = 33). RBC AA contents on day 10 were correlated (P < 0.05) with birth weight in breast-fed infants and all formula-fed infants, with on day 10 a standard deviation score (SDS) for weight, length and occipito-frontal circumference in all formula-fed infants, and with on day 10 an SDS for length in breast-fed infants. Brain weight was related to RBC DHA and CE DHA contents on both day 10 and day 42 in formula-fed infants. Of the variances of brain growth parameters on day 42, 21–34% were explained by DHA status on day 42 and protein intake from days 10–42. Conclusion We conclude that parameters of early neonatal AA status are related to intra-uterine rather than to post-natal growth. Parameters of post-natal brain growth are related to RBC DHA and CE DHA contents on day 42, and to dietary protein intake. These results point to the importance of dietary DHA for brain growth in the first 6 post-natal weeks.