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Obesity and cardiovascular diseases are prominent in the African American population. The immune system is key in the development of these diseases, and clinical evidence indicates that individuals that progress to cardiovascular disease display inflammatory markers years before the disease is openly declared. We hypothesized that obesity would lead to alterations of the circulating T lymphocyte profile and activation status in a population of African American teenagers. Lean (BMI < 50th percentile) and obese (BMI ≥ 95th percentile) African American teenagers (14-20 years-old; n=13-22/group) of both genders were recruited from public schools of Augusta, GA. Circulating immune cell phenotypes and activation status were analyzed by fluorescence-activated cell sorting (FACS), and total whole blood cell counts with 5 differentials (neutrophils, lymphocyte, monocyte, eosinophils and basophils) were also determined. Results are expressed as absolute numbers ± SD (x 105 cells/ml). When compared to lean counterparts, obese individuals presented significantly elevated numbers of circulating T lymphocytes (CD3+ cells (x 105 cells/ml): 174.6±65 vs. 148.3±53.1), T helper cells (CD4+ cells (x 105 cells/ml): 170.7±60.6 vs. 144.3±47) and activated T lymphocytes (CD3+/CD69+ cells (x 105 cells/ml): 5.62±7.5 vs. 3.78±3.7). A sex stratified analysis of the data further indicated that obese males had significantly elevated numbers of circulating CD4+ cells (163±51 x 105 cells/ml) compared to lean males (136.4±47.0 x 105 cells/ml), while obese females presented elevated numbers of T lymphocytes (176.6±68.5 vs. 150.8±51 x 105 cells/ml), T helper cells (175±65 vs. 150.6±46.3 x 105 cells/ml) and activated T cells (CD3+/CD69+: 6.8±8.9 vs. 4.2±4.5 x 105 cells/ml) and T cytotoxic cells (CD8+/CD69+: 3.9±4.0 vs. 2.8±2.1 x 105 cells/ml) when compared to lean females. In conclusion, obesity in African American teenagers produces an imbalance in the circulating T cell profile, leading to an elevation in T lymphocyte numbers, and, specifically in female individuals, to the activation of T cells and T cytotoxic cells. The identification of this obesity-related T-cell activation may provide new etiologies and biomarkers for obesity-induced cardiovascular disease.