From the OGTT, glucose and insulin IAUC were 29.1 and 22.5% lower (P = 0.01) in African-Americans compared with Latino adolescents. From the IVGTT, insulin sensitivity and glucose effectiveness were 41.7% (P < 0.01) and 50.0% (P = 0.02) lower in African-Americans compared to Latinos. AIR (P = 0.001) and disposition index (P = 0.02) were 63.0 and 48.8% higher in African-Americans, respectively, compared with Latinos. These findings persisted after controlling for body composition and fat distribution.