Background: It has been suggested that the association between birthweight and blood pressure has been overstated as a result of publication bias and, within studies, a lack of adjustment for potentially important maternal and socioeconomic confounding factors and 'overadjustment' for current body size. This study investigates the impact of potential confounding variables on the birthweight-blood pressure association in birth cohort studies from different time periods and geographical locations in Europe. Methods: Data from five European birth cohort studies (from Finland, the UK, and the Faroe Islands) taking part in the European Birth-Lifecourse-Studies (EURO-BLCS) project were analysed. Birthweight was measured at birth in all cohorts and confounding variable information was collected prospectively at subsequent follow-ups in all cohorts. Regression models were used to assess the unadjusted association between birthweight and blood pressure and then to assess the impact of potential maternal and socio-economic confounding variables and adjustment for later body size. Analyses were carried out in the same way across all five cohorts. Results: Birthweight was consistently negatively associated with systolic blood pressure (SBP) across all cohorts. Gestational age and possibly maternal pre-pregnancy weight, but not socioeconomic status, may be important confounding factors of the relationship between birthweight and SBP. The size of the birthweight-SBP association in adulthood may be larger than in childhood before adjustment for current body size, although a cohort effect cannot be ruled out. Conclusion: This study highlights the value of future cross-cohort comparisons in the investigation of the foetal origins of adult disease.