Preterm birth and low birth weight have been associated with an increased risk of hypertension; postnatal growth and dietary salt intake may contribute to these associations. In adults, the change of blood pressure (BP) in response to modifications in salt intake, i.e., salt sensitivity of BP, has been independently associated with cardiovascular disease. Little is known about salt sensitivity in children. We hypothesize that it may partly explain the association between preterm birth and higher BP in later life. We assessed salt sensitivity of BP at age 8 years in 63 preterm-born children, and explored its association with postnatal growth, sodium intake, and body composition from infancy onwards. BP was measured at baseline and after a 7-day high-salt diet. The difference in mean arterial pressure (MAP) was calculated; salt sensitivity was defined as an increase in MAP of ≥5%. Ten children (16%) showed salt sensitivity of BP, which was associated with neonatal growth restriction as well as with lower fat mass and BMI from infancy onwards. At age 8 years, children classified as salt sensitive had a lower weight-for-age SD-score (-1.5 ± 1.3 vs. -0.6 ± 1.1) and BMI (13.8 ± 1.7 vs. 15.5 ± 1.8 kg/m2) compared to their salt resistant counterparts. Sodium intake was not associated with (salt sensitivity of) BP. Salt sensitivity of BP was demonstrated in preterm-born children at age 8 years and may contribute to the development of cardiovascular disease at later age. Long-term follow-up studies are necessary to assess reproducibility of our findings and to explore clustering with other cardiovascular risk factors.