In this study, lymphocyte subgroups including blood CD3, CD4, CD8, CD4/CD8, CD19, and CD16.56 values were analyzed in children with Down syndrome (DS). The study includes 85 children with DS, followed at Department of Pediatrics, Faculty of Medicine, Yuzuncu Yil University and 64 healthy age-matched control participants. Blood CD3, CD4, CD8, CD4/CD8, CD19, and CD16.56 values were examined in both the groups. Significantly decreased blood CD3, CD4, and CD19 values were found in the study group (P < .05) when compared with the control group. In conclusion, we would like to emphasize that blood CD3, CD4, and CD19 levels were found to be decreased in children with DS. Based on these finding, we think that these decreased lymphocyte subgroups might be responsible for increased susceptibility to infections in children with DS.