Nutritional exposures in early life can have a long-lasting effect on cardiovascular disease (CVD) risk in adulthood. However, few specific dietary factors have been identified, and the time windows when they are more likely to influence later CVD risk are uncertain. Fatty acids, especially long-chain polyunsaturated fatty acids, have well-recognized effects on CVD risk factors in adults, but their roles in early life remain unknown. The goal of this study is to study the associations of serum fatty acid concentrations during infancy and childhood with 1) BMI trajectories from infancy through adolescence and 2) cardiometabolic risk factors at age 16 y in a well-established cohort of Chilean children.