Abstract: The aim of this study was to determine the number of FoxP3+ regulatory T (Treg) cells in the microenvironment of lower lip squamous cell carcinomas (LLSCCs) and to correlate the findings with clinicopathological parameters (tumor size/extent, regional lymph node metastasis, clinical stage, and histopathological grade of malignancy). Fifty cases of LLSCC were selected. Lymphocytes exhibiting nuclear immunostaining for FoxP3 were quantified in 10 microscopic fields at the deep invasive front of LLSCCs. The results were analyzed statistically using the nonparametric Mann-Whitney test and Fisher's exact test. FoxP3+ lymphocytes were observed in all cases studied. The number of these cells tended to be higher in smaller tumors, tumors without regional lymph node metastasis, and tumors in early clinical stages, but the difference was not statistically significant (p > 0.05). Low-grade tumors contained a larger number of FoxP3+ lymphocytes than high-grade tumors (p = 0.019). Tumors with an intense inflammatory infiltrate exhibited a larger number of Treg cells (p = 0.035). On the other hand, the number of FoxP3+ lymphocytes was smaller in tumors arranged in small cell clusters (p = 0.003). No significant differences in the number of FoxP3+ lymphocytes were observed according to the degree of keratinization (p = 0.525) or nuclear pleomorphism (p = 0.343). The results suggest the participation of Treg cells in immune and inflammatory responses in the microenvironment of LLSCCs. These cells may play a more important role in early stages rather than in advanced stages of lip carcinogenesis.