Background: Although the relation of salt intake with blood pressure (BP) is linear, it is U–shaped for mortality and cardiovascular disease (CVD). This individual-participant meta-analysis explored whether the relation of hypertension, death or CVD with 24-h urinary sodium excretion (UVNA) or sodium-to-potassium (UNAK) ratio was modified by birth weight. Methods: Families were randomly enrolled in the Flemish Study on Genes, Environment and Health Outcomes (1985–2004) and the European Project on Genes in Hypertension (1999–2001). Categories of birth weight, UVNA and UNAK (≤2500, >2500–4000, >4000 g; <2.3, 2.3–4.6 and >4.6 g; and <1, 1–2, >2, respectively) were coded using deviation-from-mean coding and analyzed by Kaplan–Meier survival functions and linear and Cox regression. Results: The study population was subdivided into the Outcome (n = 1945), Hypertension (n = 1460) and Blood Pressure cohorts (n = 1039) to analyze the incidence of mortality and cardiovascular endpoints, hypertension and BP changes as function of UVNA changes. The prevalence of low/medium/high birth weight in the Outcome cohort was 5.8/84.5/9.7%. Over 16.7 years (median), rates were 4.9, 8 and 27.1% for mortality, CVD and hypertension, respectively, but were not associated with birth weight. Multivariable-adjusted hazard ratios were not significant for any endpoint in any of the birth weight, UVNA and UNAK strata. Adult body weight tracked with birth weight (P < 0.0001). The partial r in the low-birth-weight group associating changes from baseline to follow-up in UVNA and SBP was 0.68 (P = 0.023) but not significant in other birth weight groups. Conclusion: This study did not substantiate its prior hypothesis but showed tracking of adult with birth weight and suggest that low birth weight increases salt sensitivity.