Este artigo é resultante da Dissertação apresentada pelo autor Artur Kautzmann Filho ao Programa de Pós-Graduação em Pediatria e Saúde da ABSTRACT Aims:To evaluate neutrophil migration and the relative frequency of CD4+/CD8+ lymphocytes in children with Down syndrome and in healthy controls. Methods: This was a case-control study carried out at the Institute of Biomedical Research, affiliated with São Lucas Hospital of the Pontifical Catholic University of Rio Grande do Sul (PUCRS). Patients with Down syndrome were selected by convenience sampling, including all children with Down syndrome aged 3 to 13 years treated at the Pediatric and Otolaryngology Outpatient Clinics of São Lucas Hospital and at KinderCenter for Children with Special Needs, in Porto Alegre, State of Rio Grande do Sul, Brazil, between January and December 2012. Healthy children without Down syndrome, participants in another ongoing study conducted by Institute of Biomedical Research, were recruited to the control group. Those patients with the largest volume of cells stored in cryotubes were selected. A neutrophil chemotaxis assay and immunophenotyping of CD4+ and CD8+ T cells were performed to evaluate the functionality of the immune response. Associations were assessed by the chi-squared test, Student's t test, or Mann-Whitney's test. All tests were bidirectional, and p values less than 0.05 were regarded as statistically significant. Results: This study included 19 patients (13 with Down syndrome and six controls), with a mean age of 8.13 and 9.83 years, respectively. No significant changes concerning neutrophil migration were observed in the Down syndrome group. However, patients with Down syndrome tended to have a lower rate of CD4+ T cells and a higher rate of CD8+ T cells. The CD4+/CD8+ ratio revealed significant difference between the groups, being lower in patients with Down syndrome. Conclusions: This study suggests that patients with Down syndrome show a decreased CD4+/CD8+ ratio, which may contribute to the frequent and recurrent infections in these children.KEY WORDS: down syndrome; immunity; CD4-CD8 ratio; child; infection. Scientia Medica Artigo originAlOpen Access 2015;25(1):ID19235 ISSN 1980ISSN -6108 : http://dx.doi.org/10.15448/1980ISSN -6108.2015 Recebido: novembro,