Background: Although, odontogenickeratocyst (OKC) and dentigerous cyst (DC) are considered asdevelopmental cysts inflammation has been seen in its connective tissue wall. Inflammation is seen to alter the epithelial lining of both OKC and DC butwhether it plays in altering the behavior of these cysts is not fully understood. Aim: The present study is conducted with the help of molecular marker proliferating cellular nuclear antigen (PCNA) to assess the proliferative activity of OKC and DC and to further evaluate and correlate the effect of inflammation on the proliferative activity and hence on biological behavior of these cysts. Materials and Methods: Immunohistochemicalstaining was performed using antiâPCNA antibody in 10 cases each of classical OKC, inflamed OKC, classical DC, and inflamed DC. The resulting data was tabulated on Microsoft excel and subjected to statistical analysis using twoâway analysis of variance test, t test and post-hoc test followed by Bonferroni test with the application of statistical package for social sciences (SPSS) (SPSS, Chicago, IL, USA) and EpiâInfo 6.04 d, Atlanta, Georgia (USA). Results: Total mean PCNA expression is statistically higher in inflamed OKC than classical OKC and inflamed DC also showed significantly higher PCNA expression than classical DC (P < 0.001). Correlation between inflammation and PCNA expression was not statistically significant (P ≥ 0.05). Conclusion: Inflammation is responsible for change in behavior of neoplastic epithelium of OKC, whereas in dentigerous it is responsible for changes in epithelial lining and hence should be treated meticulously.