Endocervical adenocarcinomas (ECAs) and endometrial adenocarcinomas (EMAs) are malignancies that affect the uterus; however, their biologic behaviors are quite different. This distinction has clinical significance, because the appropriate therapy may depend on the site of tumor origin. In this study, we not only compare the individual expression status of 4 immunomarkers [estrogen receptor (ER), vimentin (Vim), carcinoembryonic antigen (CEA), and p16], but also evaluate whether p16 adds value to the ER/Vim/CEA panel characteristics and performance in distinguishing between primary ECA and EMA. A tissue microarray (TMA) was constructed using paraffin-embedded, formalin-fixed tissues from 38 hysterectomy specimens, including 14 ECAs and 24 EMAs. Tissue microarray sections were immunostained with 4 antibodies, by the avidin-biotin complex method for antigen visualization. The staining intensity and area extent of the immunohistochemical reactions were evaluated using the semiquantitative scoring system. The 3 markers (ER, Vim, CEA) and their respective panel expressions showed statistically significant (P<0.05) frequency differences in ECA and EMA tumors. The p16 marker also revealed a significant frequency difference (P<0.05) between ECA and EMA, but did not demonstrate any supplementary benefit to the traditional 3-marker panel. In conclusion, when histomorphologic and clinical doubt exist as to the primary site of origin, we suggest that the conventional 3-marker (ER/Vim/CEA) panel is appropriate. Ancillary p16-marker testing does not add value to the 3-marker panel in distinguishing between primary ECA and EMA.