BACKGROUND: Early epidemiological studies have associated low birthweight with increased cardiovascular risk. We aimed to examine whether the fat and fat-free components of birthweight have differing relationships with childhood cardiovascular risk markers. METHODS: In the Growing Up in Singapore Towards healthy Outcomes (GUSTO) cohort, air displacement plethysmography was conducted within 24 h after delivery in 290 naturally conceived singletons. We investigated associations of newborn cohort-specific standardized z-score of fat mass, fat-free mass, body fat percentage and birthweight on child (at 6 years of age) carotid intima-media thickness, pulse wave velocity, blood pressure, prehypertension/hypertension (>110/70 mmHg) and standardized systolic and diastolic blood pressure (SBP and DBP) trajectories (at 3-6 years of age), taking account of maternal education, height, tobacco exposure, parity, ethnicity, child's sex, gestational age, age at follow-up, and other maternal factors. RESULTS: Clear inverse associations were seen for blood pressure with z-score of fat mass [SBP, β (95% CI): -1.31 mmHg (-2.57, -0.06); DBP: -0.79 mmHg (-1.74, 0.15)] and body fat percentage [SBP: -1.46 mmHg (-2.73, -0.19); DBP: -0.80 mmHg (-1.75, 0.16)], but not with fat-free mass [SBP: 0.27 mmHg (-1.29, 1.83)]; DBP: -0.14 mmHg (-1.30, 1.03)]. Being in the lowest tertile of fat mass or body fat percentage was associated with higher blood pressure trajectories and prehypertension/hypertension risk [OR (95% CI), fat mass: 4.23 (1.41, 12.68); body fat percentage: 3.22 (1.09, 9.53)] without concomitantly higher overweight/obesity risk. CONCLUSIONS: At birth, low adiposity was associated with increased childhood blood pressure. Low newborn adiposity might serve as a marker of poor fetal growth or suboptimal intrauterine conditions associated with hypertension risk later in life.