Objective: There are microscopic similarities among odontogenic keratocyst (OKC), orthokeratinized odontogenic keratocyst (DOC) and epidermal cyst (EDC). This study was to compare with cell proliferation, cell differentiation and apoptosis related factors in OKC, DOC and EDC in order to clarify the characters and category of three hitstopathologically similar cysts.Material and Methods: Fourteen cases of OKC, nine cases of DOC and eighteen cases ofEDC were examined immunohistochemically using antibodies against cytokeratins (CK7,10, 10/13,17,18,19,20) and apoptosis related factors (bcl-2 and Bax).Results: Ki-67 labeling index in OKC was statistically higher than that in DOC and EDC (p<0.05). And that in DOC was higher in EDC (p<0.05). In OKC, CKs and bcl-2 expression patterns were different from DOC and EDC, while both DOC and EDC showed similar reactivity with CKs and bcl-2.Conclusions: The present results suggested that OKC had high cellular proliferation and was relatively low differentiation as compare with DOC and EDC. In addition, there was participation of apoptosis suppressor in OKC. The character of DOC occupied an intermediate position between OKC and EDC. Therefore, it was possible to consider DOC as a distinct entity from OKC. EDC had the lowest cellular activity in the three cysts and it was comparatively maturated lesion.