Background The use of PTEN, PCNA, and β-catenin may be of value to differentiate well differentiated endometrioid carcinoma from complex atypical endometrial hyperplasia. Methods Immunohistochemical evaluation of PTEN, PCNA, and β-catenin was performed on 100 specimens including eight proliferative endometrium, 10 secretory endometrium, 10 simple endometrial hyperplasia, 10 complex typical endometrial hyperplasia, 30 complex atypical endometrial hyperplasia, and 32 endometrioid adenocarcinoma. Immunostaining of cells was analysed by arbitrary semiquantitative methods according to both slides staining area and intensity of colour reaction. Findings PTEN was expressed in 100% of proliferative endometrium, 0% of secretory endometrium, 60% of simple typical hyperplasia, 100% complex typical hyperplasia, 46.7% complex atypical hyperplasia, and 37.5% endometrioid adenocarcinoma. There was a significant difference in PTEN expression between complex atypical endometrial hyperplasia and endometrioid adenocarcinoma. PCNA was expressed in 50% of proliferative endometrium, 40% of secretory endometrium, 80% of simple endometrial hyperplasia, 100% of complex typical hyperplasia, 46.7% of complex atypical hyperplasia, and 87.5% of endometrioid adenocarcinoma. There was a significant difference in PCNA expression between complex atypical endometrial hyperplasia and endometrioid adenocarcinoma. β-catenin was expressed in the membrane and the cytoplasm of 100% of proliferative endometrium, 100% of secretory endometrium, 100% of simple endometrial hyperplasia, 100% of complex typical hyperplasia, 60% of complex atypical hyperplasia, and 81.25% of endometrioid adenocarcinoma. Nuclear staining was noted in 33.3% of complex atypical hyperplasia and 37.5% of endometrioid adenocarcinoma; 83.3% and 16.7% of positive nuclear staining cases were well differentiated and poorly differentiated adenocarcinoma respectively. There was a significant difference in β-catenin expression between complex atypical hyperplasia and endometrioid carcinoma, but the difference in nuclear β-catenin between endometrioid carcinoma and complex atypical hyperplasia was not significant. Interpretation PTEN, PCNA, and β-catenin could be of value to differentiate complex atypical endometrial hyperplasia from endometrioid adenocarcinoma, but nuclear β-catenin is of no such value