Background: Age-related changes in proliferative activity in human gingival epithelium are uncertain. Proliferating cell nuclear antigen (PCNA) is a nuclear protein associated with the cell cycle. Nuclear PCNA immunoreactivity is found in the proliferative compartment of normal tissues. The aims of this study were to investigate the localization of PCNA expression in oral gingival epithelium (OGE) and to define the age-related changes as to PCNA-proliferative index (PI) in inflamed as well as healthy gingiva. Mitotic index (MI) was also used as a conventional marker of cell proliferation. Additionally, the effect of aging upon the maximum epithelial thickness (MET) was determined.