The aim of this study is to investigate the effects of age and gender on relative number of CD4+ and CD8+ T lymphocyte and CD4+/CD8+ ratios in gingival tissue and peripheral blood of periodontally healthy BALB/c mice with flow cytometric analysis. The study was carried out on periodontally healthy 60 BALB/c mice. They were separated into five groups according to the life expectancy: Group I (newborn, 1-10 days old), Group II (age at weaning, 21-28 days old), Group III (age of sexual maturity, puberty, 7-8 weeks old), Group IV (adult, 8 months old), and Group V (the aged, 14 and over). Males and females were equally represented in each group. CD4+ and CD8+ T lymphocytes and CD4+/CD8+ ratio values in gingival tissue and peripheral blood were determined using flow cytometry in the biopsy samples. The relative number of CD8+ T lymphocyte in gingival tissue was higher in puberty (p < 0.05) and the aged (p < 0.05), with more significantly difference in males (p < 0.05). The CD4+/CD8+ ratios in gingival tissue were lower in puberty group and the-aged groups compared to the other groups (p < 0.05). The peripheral blood CD4+/CD8+ ratio increased in puberty and the aged groups. These differences were more significant in females than in males (p < 0.05). There were considerable negative correlations between CD4+/CD8+ T lymphocyte ratio in gingival tissue and CD4+/CD8+ T lymphocyte ratio in peripheral blood in puberty (r = 0.647, p < 0.01) and the aged ( r = 0.599, p < 0.05). In conclusion, our data suggest that CD4+/CD8+ T lymphocyte ratios in peripheral blood increase periodontally healthy mice in puberty and the old groups, while CD4+/CD8+ T lymphocyte ratios in gingival tissue decrease in the same groups. The relative number of CD8+ T lymphocytes increases in gingival tissue in puberty and the old groups when it decreases in peripheral blood. Results from this study indicated that periodontally healthy BALB/c mice may represent important information to determine the character of an immune response in the course of a lifetime.