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Physiological evidence suggests that birth weight (BW) and postnatal growth affect blood pressure (BP) level, independently or in interaction. Their respective roles are difficult to disentangle in epidemiological studies, however, especially when adjusting for final weight. We assessed the portion of the effect of BW on BP at 5 years that was not attributable to postnatal growth and investigated potential interactions between BW and postnatal growth velocity at different time points in the EDEN mother–child study. Collecting a median of 19 weight measurements for each of the 1119 children who completed follow-up enabled us to model instantaneous growth velocity at any age. After computing a BP SD-score at 5 years, adjusted for age, sex, current body mass index, and height, we used multiple linear regression to study its association with age- and sex-specific BW z score, adjusting for several maternal and pregnancy risk factors. We tested interactions between BW categories (small-, appropriate-, and large-for-gestational-age) and weight growth velocities at different ages. The BW z score was negatively and significantly correlated with the systolic BP SD-score at the age of 5 years (r=−0.07, P=0.02). Interactions were found between BW categories and weight growth velocities from 1 to 4 months (P from 0.002 to 0.08) but not at older ages; specifically, children born small for gestational age with a fast weight growth velocity in their first few months of life had the highest absolute systolic BP and SD score values at 5 years. They may need monitoring for cardiovascular risks.