The association between birth size and cardiometabolic disease risk may be U-shaped. Being born small for gestational age (SGA) has a definitive association with later cardiovascular risk, but the impact of being born large for gestational age (LGA) on cardiometabolic health is more controversial. In addition to birth size, early postnatal growth pattern and later weight gain affect cardiometabolic risk in adulthood. Most SGA-born children have catch-up and LGA-born children have catch-down growth during the first years of life. The extent of this early compensatory growth may contribute to the adverse health outcomes. Both SGA- and LGA-born children are at an increased risk for overweight and obesity. This may have a long-term impact on cardiometabolic health as overweight tends to track to adulthood. Other cardiometabolic risk factors, including alterations in glucose metabolism, dyslipidemia, hypertension, and low-grade inflammation are associated with birth weight. Many of these risk factors are related to overweight or adverse fat distribution. Since later cardiometabolic risk is often mediated by early growth pattern and later overweight in SGA and LGA children, it is important to focus on staying normal weight throughout life. Hence, effective interventions to reduce cardiometabolic risk in LGA and SGA children should be developed.