Purpose: Denture-induced fibrous inflammatory hyperplasia (FIH) occurs around the borders of an ill-fitting denture. There has been no report in the literature concerning epithelial proliferative activity in FIH. The purpose of this study was to observe the labeling of proliferating cell nuclear antigen (PCNA) and evaluate its clinicopathologic results. Materials and Methods: The labeling index (LI) was assessed by using the PCNA, a nuclear protein synthesized main ly in the G1-S stages of the cell cycle that could be det ected immunohistochemically by the monoclonal antibody PC10. The PCNA LI was assessed in FIH specimens, in clinically normal specimens 1 cm from the FIH margin (adjacent group), and in clinically normal specimens located at least 2 cm from the adjacent group; the last were considered the control group. Results: The mean PCNA LI values in the basal, parabasal, and overall epithelial layers were similar in FIH and in the adjacent group and were significantly higher than in the control group. Conclusion: These data support the importance of the surgical treatment of FIH with wide excision (about 1 cm) since the clinically normal tissue around the lesion could be histologically altered.