Objective To determine whether supplementation of infant formula milk with long chain polyunsaturated fatty acids (LCPUFAs) influences blood pressure in later childhood. Design Follow up of a multicentre, randomised controlled trial. Setting Four study centres in Europe. Participants 147 formula fed children, with a reference group of 88 breastfed children. Intervention In the original trial newborn infants were randomised to be fed with a formula supplemented with LCPUFAs (n=111) or a formula without LCPUFAs but otherwise nutritionally similar (n=126). In the present follow up study the blood pressure of the children at age 6 years was measured. Main outcome measures Systolic, diastolic, and mean blood pressure. Results 71 children in the LCPUFA supplementation group (64% of the original group) and 76 children in the non-supplementation group (60%) were enrolled into the follow up study. The LCPUFA group had significantly lower mean blood pressure (mean difference - 3.0 mm Hg (95% confidence interval - 5.4 mm Hg to - 0.5 mm Hg)) and diastolic blood pressure (mean difference - 3.6 mm Hg ( - 6.5 mm Hg to - 0.6 mm Hg)) than the non-supplementation group. The diastolic pressure of the breastfed children (n=88 (63%)) was significantly lower than that of the non-supplemented formula group but did not differ from the LCPUFA formula group. Conclusions Dietary supplementation with LCPUFAs during infancy is associated with lower blood pressure in later childhood. Blood pressure tends to track from childhood into adult life, so early exposure to dietary LCPUFAs may reduce cardiovascular risk in adulthood.