Background: Epigenetic changes in visceral adipose tissue (VAT) with obesity and their effects on gene expression are poorly understood, especially during emergent obesity in youth. The current study tested the hypothesis that methylation and gene expression profiles of key growth factor and inflammatory pathways such as PI3K/AKT signaling are altered in VAT from obese compared to non-obese youth. Methods: VAT samples from adolescent females grouped as Lean (L; n=15; age=15±3 yrs, BMI=21.9±3.0 kg/m 2 ) or Obese (Ob; n=15, age=16±2 yrs, BMI=45.8±9.8 kg/m 2 ) were collected. Global methylation (n=20) and gene expression (N=30) patterns were profiled via microarray and interrogated for differences between groups by ANCOVA (p<0.05), followed by biological pathway analysis. Results: Overlapping differences in methylation and gene expression in 317 genes were found in VAT from obese compared to lean groups. PI3K/AKT Signaling (p=1.83x10 -6 ; 10/121 molecules in dataset/pathway) was significantly overrepresented in Ob VAT according to pathway analysis. mRNA upregulations in the PI3K/AKT Signaling Pathway genes TFAM (p=0.03; Fold change=1.8) and PPP2R5C (p=0.03, FC=2.6) were confirmed via qRT-PCR. Conclusion: Our analyses show obesity-related differences in DNA methylation and gene expression in visceral adipose tissue of adolescent females. Specifically, we identified methylation site/gene expression pairs differentially regulated and mapped these differences to PI3K/AKT signaling, suggesting that PI3K/AKT signaling pathway dysfunction in obesity may be driven in part by obesity-related changes in DNA methylation.Subjects. Adolescent (age 12-19) females grouped as either Lean (L; body mass index (BMI) <25; n=15) or Obese (Ob, BMI >35; n=15) were recruited to participate in this study. Three races (African-American, Caucasian and Hispanic) were represented in equal numbers (5 L; 5 Ob each). Lean patients were recruited from non-bariatric abdominal surgeries (appendectomies and cholecystectomies), while subjects with obesity were recruited prior to bariatric surgery at Children's National Medical Center. Known clinical diagnoses and medications at the time of surgery are listed below per group -N=1 per diagnosis/medication unless otherwise noted. Lean cohort: sickle cell anemia, localized peritonitis, ulcerative colitis, Crohn's disease, acid reflux, Remicade (n=2), Albuterol, and prednisone. Obese cohort: asthma (n=4), sleep apnea (n=3), insulin resistance, hypertension, polycystic ovary syndrome, appendicitis, cholecystitis, sickle cell trait, pseudotumor cerebri, hypothyroidism, albuterol, prednisone, Lisinopril, levothyroxine, and Diamox. Bariatric surgery patients had completed a protein-sparing modified fast (~1000 kcal/day; 50-60 g protein) for two weeks prior to their date of surgery. All operations took place after a minimum 12-hour overnight fasting per standard surgical practices. Patients provided assent and legal guardians signed written informed consents as approved by the Children's National Medical Center ...