Cell proliferation markers play an important role in the biological behavior of neoplasms. This study investigated the immunohistochemical expression of PCNA, Ki-67 and Cyclin B1 proteins based on the pattern of cell invasion in oral squamous cell carcinoma (OSCC). A total of 39 OSCC specimens and 13 samples of normal oral mucosa (control) were immunohistochemically analyzed. Protein expression was evaluated according to World Health Organization – Histological Malignancy Grading (WHO-HMG) and a specific grading system for invasion, graded from 1 to 4, varying from a consistently well-defined “pushing” border to diffuse infiltration and cellular dissociation, and was then correlated with clinical features. We found higher expression of Ki-67 and Cyclin B1 in OSCC when compared with the control group. High Ki-67 expression levels were more commonly seen in the floor of the mouth than in the tongue (P = 0.009). Cyclin B1 showed a positive correlation with histological grade, according to WHO-HMG criteria (P = 0.01). Our results suggest that Cyclin B1 is a reliable proliferation marker for indicating degree of tumor proliferation. Correlations between PCNA, Ki-67, Cyclin B1 and invasive tumor front with overall survival were not observed. Further studies are needed in order to elucidate whether cell proliferation activity at the tumor invasion front is related to prognosis. (J Oral Sci 52, 417-424, 2010)