Abstract Objective To evaluate insulin resistance (IR), β-cell function, and glucose tolerance in 119 Brazilian adolescents with obesity or risk factors (RF) for type 2 diabetes mellitus (T2DM). Study Design We analyzed weight (kg), height (m), body mass index (BMI; kg/m 2), waist (W; cm), acanthosis nigricans (AN), systolic and diastolic blood pressure (SBP and DBP; mm Hg), fasting plasma glucose (FPG), and 2-h plasma glucose (2hPG) on oral glucose tolerance test (OGTT; 1.75 g of glucose/weight), lipid profile [total cholesterol (TC), fractions, and triglycerides (TGs)], fasting insulin (FI) and 2-h insulin on OGTT (2hI-RIA), HOMA-B (%; β-cell function—HOMA program), HOMA-S (%; insulin sensitivity—HOMA program) and HOMA-IR [fasting plasma insulin (mU/ml)×fasting plasma glucose (mmol/L)/22.5]. Division according to number of RF—family history of T2DM (FHT2DM), obesity, hypertension, dyslipidemia, polycystic ovary syndrome (PCOS), and AN. G1: subjects with no or one RF; G2: subjects with two or more RFs. Statistical data were nonparametrical. Results Fasting plasma glucose (G2: 81.6±10.2 vs. G1: 79.8±9.9 mg/dl) and 2hPG (88.1±18.0 vs. 87.0±19.9 mg/dl) were not different between G2 ( n=67) and G1 ( n=52), and all adolescents had normal glucose tolerance (NGT). Fasting insulin (13.0±7.9 vs. 7.6±3.9 μIU/ml; P<.001) and 2hI (60.2±39.1 vs. 38.3±40.0 μIU/ml; P<.001), HOMA-B (169.1±131.6% vs. 106.1±39.9%; P<.001), and HOMA-IR (2.62±1.7 vs. 1.52±0.8; P<.001) were higher in G2. HOMA-S (92.5±59.5% vs. 152.2±100.5%; P<.001) was also lower in this latter group. Conclusion Brazilian adolescents with two or more RFs for the development of T2DM have higher IR and β-cell function and lower insulin sensitivity. However, adolescents with impaired glucose tolerance (IGT) or DM have not been found, differently from similar studies. Differences in ethnic background, environment, and lifestyle factors may account for this disparity.