BACKGROUND: Childhood obesity is associated with insulin resistance (IR), increased levels of small dense low-density lipoprotein (sd-LDL) as well as with augmented hepatic de novo lipogenesis, which implies increased triose phosphate fluxes that may lead to increased methylglyoxal (MG) and its catabolic end product D-lactate. We hypothesized that obese adolescents have increased D-lactate serum levels associated with high incidence of sd-LDL. METHODS: This is a cross-sectional study where the anthropometric characteristics, atherogenic dyslipidemia complex, sd-LDL (Lipoprint, Quantimetrix) and D-lactate (kinetic enzymatic analysis) were explored in 30 lean vs. 30 obese adolescents (16 females and 14 males per group) without metabolic syndrome (MetS). Endothelial function by flow-mediated dilation (FMD, by ultrasound) and arterial lesion by carotid intima media thickness (CIMT, by ultrasound) were also measured. RESULTS: The mean age of participants was 16.8 ± 1.4 years. Obese adolescents had a body mass index of 32.7 ± 3.8 vs. 21.8 ± 2.1 in lean participants. The obesity group showed higher D-lactate levels: 6.2 ± 3.0 vs. 4.5 ± 2.5 µmol/L, higher levels of insulin: 15 (9.6-23.5) vs. 7.9 (6.5-10.5) µIU/mL; triglyceride (TG): 1.46 (1.1-1.8) vs. 0.84 (0.6-1.2) mmol/L; non-high-density lipoprotein-cholesterol (NON-HDL-C): 2.8 ± 0.9 vs. 2.3 ± 0.7 mmol/L; total cholesterol (TC)/HDL-C) index: 2.9 ± 0.7 vs. 2.4 ± 0.5; TG/HDL-C index: 2.2 (1.5-2.8) vs. 1.1 (0.8-1.8); %LDL-3: 4.2 ± 4.07 vs. 1.9 ± 2.7; smaller LDL size: 270.6 ± 3 vs. 272.2 ± 1.1 Å. D-lactate correlated positively with LDL-2: r = 0.44 and LDL-3 (sd-LDL): r = 0.49 and negatively with large LDL-1: r = -0.48 and LDL size: r = -0.46; (p<0.05, p<0.01, p<0.001 and p<0.0001, respectively). Obese adolescents showed higher CIMT: 0.51 ± 0.08 vs. 0.46 ± 0.08 mm and lower FMD: 20.3% ± 6.7% vs. 26.0% ± 9.3%. CONCLUSIONS: Obese adolescents display subclinical signs of IR and endothelial dysfunction. Higher serum sd-LDL levels correlated positively with D-lactate levels. These findings suggest an association between atherogenic dyslipoproteinemia and whole body MG fluxes already detectable in apparently healthy obese adolescents.