It is often hard to differentiate among adenocarcinoma in situ and early invasive endocervical adenocarcinoma. Little is known of the immunohistochemical changes associated with the invasion of endocervical adenocarcinoma. The aim of this study was to examine the phenotypic changes associated with the epithelial-mesenchymal transition in adenocarcinoma in situ and invasive adenocarcinoma of the uterine cervix. The immunohistochemical expression of vimentin, smooth-muscle actin, CD34 and E-cadherin was assessed in 10 cases of normal endocervical epithelium, 10 cases of adenocarcinoma in situ and 10 cases of invasive adenocarcinoma. The intensity of the immunohistochemical expression was evaluated on a scale from 0 to 3 (0=no expression, 3=high expression). Compared to normal endocervical epithelium and AIS, there was an increase in the staining of the periglandular stroma for SMA in IAC. The expression was moderate (2) in 6/10 cases of IAC and high (3) in only one case of IAC. CD34 was strongly expressed (3) in all cases of normal endocervical epithelium and AIS. Moderate (2) CD34 expression was found in 7/10 cases of IAC and low (1) in 3/10 cases. The intensity of the expression of both SMA and CD34 correlated with the depth of invasion of atypical tumor glands. There was no difference in the immunohistochemical staining for vimentin and E-cadherin among normal endocervical epithelium, AIS and IAC. Epithelial-mesenchymal transition might be a mechanism of invasion in endocervical adenocarcinoma. However, further studies are required to determine which immunohistochemical markers could be used in the differentiation of adenocarcinoma in situ from invasive adenocarcinoma of the uterine cervix.