Background & Aims: Odontogenic cysts are derived from odontogenic epithelium and lined by odontogenic epithelium .All three odontogenic cysts (Dentigerous cyst,Odontogenic keratocyst cyst and Radicular cyst)can develop tumoral transformation .The least tumoral transformation rate is related to OKC.Epithelial cell proliferation rate is important in the prognosis .The best marker is HER2/neu.

Materials & Method: In this study 70 samples diagnosed as 3 odontogenic cysts(29 cases of Dentigerous cyst,24 cases of odontogenic keratocyst cyst and 17 cases of Radicular cyst)were selected from archive of Oral Pathology Department of Detal Faculty. The samples were prepared for IHC staining method. Data were collected and analyzed by using Fisher Exact test and SPSS version 17. Staining rate of tumoral cells were scored from 0-3.Scores 2 and 3 were considered as overexpression.

Results:Three cases of OKC and 7 case of Dentigerous cyst were negative in staining but all cases of radicular cysts were positive. Fisher Exact test showed significant difference between the scores and type of cyst (P=0.005). Overexpression was found in 41.7% of OKC,48.3% of DC and 88.2% of RC.

Conclusion: In conclusion,RC had the highest rate of staining (88.2%) which reveals the highest proliferation rate in this cyst .It can be explanation for higher rate of carcinimatous change in RC and residual periapical cyst.