Maternal (n-3) PUFA deficiency is associated with higher blood pressure (BP) later in life in rat offspring, and early intake of (n-3) PUFA in formula-fed infants was shown to modify later BP. BP, heart rate (HR), and heart rate variability (HRV) are affected by dietary (n-3) PUFA in adults. In this study, we investigated whether fish oil (FO) supplementation of lactating mothers could modify BP, pulse wave velocity (PWV), and HRV in their children after 2 y. Mothers with low fish intake were randomly assigned to FO or olive oil (OO) supplementation for the first 4 mo after delivery. A reference group of mothers with a high habitual fish intake (HFI) was also followed. At the follow-up study at 2.5 y of age, BP and PWV were measured, and electrocardiograms were recorded for 0.5 h. FO supplementation significantly increased RBC levels of long-chain (n-3) PUFA of the 4 mo-old children, but at 2.5 y, the FO and OO groups did not differ. BP, PWV, HR, and HRV also did not differ among the groups. However, for all 3 groups, the children's intake of (n-3) PUFA at 2.5 y was negatively correlated with mean arterial pressure after adjustment for outdoor temperature (r = -0.245, P = 0.04). In conclusion, maternal FO supplementation had no overall effect on BP, PWV, or HRV of the children, indicating that (n-3) PUFA intake of Danish mothers may be sufficient in this sense. However, children's dietary intake of (n-3) PUFA might have a beneficial effect on BP in childhood.