Exposure of several human populations to arsenic has been associated with a high incidence of detrimental dermatological and carcinogenic effects. To date, studies examining the immunotoxic effects of arsenic in humans, and specifically in children, are lacking. Therefore, we evaluated several parameters of immunological status in a group of children exposed to arsenic through their drinking water. Peripheral blood mononuclear cells (PBMCs) of 90 children (6 to 10 years old) were collected. Proportions of lymphocyte subpopulations, PBMC mitogenic proliferative response, and urinary arsenic levels were evaluated. Increased urine arsenic levels were associated with a reduced proliferative response to phytohemaglutinin (PHA) stimulation (P=0.005), CD4 subpopulation proportion (P=0.092), CD4/CD8 ratio (P=0.056), and IL‐2 secretion levels (P=0.003). Increased arsenic exposure was also associated with an increase in GM‐CSF secretion by mononucleated cells (P=0.000). We did not observe changes in CD8, B, or NK cell proportions, nor did we observe changes in the secretion of IL‐4, IL‐10, or IFN‐γ by PHA‐activated PBMCs. These data indicate that arsenic exposure could alter the activation processes of T cells, such that an immunosuppression status that favors opportunistic infections and carcinogenesis is produced together with increased GM‐CSF secretion that may be associated with chronic inflammation.