Studies in experimental animals and human subjects have suggested that intake of n-3 fatty acids in early life can affect cardiovascular risk factors in adult life. Therefore, the aim of the present study was to investigate the effect of fish oil (FO) supplementation during the third trimester of pregnancy on blood pressure (BP), heart rate (HR) and HR variability (HRV) in the 19-year-old offspring. The study was based on follow-up of a randomised, controlled trial from 1990, in which 533 pregnant women were randomised to FO, olive oil (OO) or no oil (NO) during the last trimester of pregnancy. The offspring was invited to a physical examination including BP, HR and HRV measurements. A subgroup consisting of the offspring of mothers with a low baseline fish intake also had 24 h HRV determined. The OO group was used as reference and multiple linear regression modelling was used to compare the FO and OO groups. A total of 180 of the offspring from the FO and OO groups agreed to participate in the study (45 %). The adjusted difference between the FO and OO groups was 2 (95 % CI − 1, 4) mmHg in systolic and 1 (95 % CI 0, 3) mmHg in diastolic BP. The difference in HR was 1 (95 % CI − 2, 4). Also, HRV indices did not differ significantly between groups. Hence, FO supplementation during late pregnancy was not associated with offspring BP, HR and HRV during adolescence.