Objective: Relative to whites, African Americans have lower circulating triglycerides (TG) and greater high-density lipoprotein cholesterol. The metabolic basis for this difference is not known. This study was conducted to test the hypothesis that insulin-induced suppression of free fatty acids (FFA) results in lower serum TG in African American versus white prepubertal children. Research Methods and Procedures: Insulin, FFA, and TG were determined at baseline and during a frequently sampled, intravenous glucose tolerance test in eight African American and eight white prepubertal males pair-matched for whole-body insulin sensitivity. Results: Baseline TG was lower in African Americans (0.43 ± 0.10 vs. 0.79 ± 0.37 mM/L; mean ± SD; p < 0.01). African Americans had higher peak insulin (218 ± 102 vs. 100 ± 30 pM/L; mean ± SD; p < 0.01) and a greater acute insulin response (9282 ± 4272 vs. 4230 ± 1326 pM/L × 10 minutes; mean ± SD; p < 0.05). FFA and TG values determined at the FFA nadir were lower in African Americans (0.26 ± 0.02 vs. 0.30 ± 0.03 mEq/L; mean ± SD; p < 0.01 for FFA nadir and 0.49 ± 0.07 vs. 0.77 ± 0.33 mM/L; mean ± SD; p < 0.05 for TG). Among all subjects, FFA nadir was correlated with peak insulin (r = -0.54; p < 0.05). After adjusting for FFA nadir, neither baseline nor postchallenge TG differed with ethnicity (p = 0.073 and 0.192, respectively). The ethnic difference in FFA nadir disappeared after adjusting for peak insulin (p = 0.073). Discussion: These data suggest that hyperinsulinemia-induced suppression of FFA among African Americans is a determinant of lower TG in this group.