The natural history of cervical adenocarcinoma is largely unknown, and whether endocervical glandular dysplasia is a precursor lesion to malignant tumor formation is a controversial issue. The aim of this study was to clarify the relationship of endocervical glandular dysplasia to the uterine endocervical adenocarcinoma. Thirty-one cases of glandular abnormalities of the uterine cervix were identified histologically from January 1984 to April 1992. These included 11 cases of endocervical glandular dysplasia, 5 cases of adenocarcinoma in situ, 4 cases of microinvasive adenocarcinoma, and 11 cases of invasive adenocarcinoma. The immunohistochemical localization of epithelial-specific antigen (ESA) was examined in these cases of endocervical glandular dysplasia and related lesions, and was compared to 10 normal endocervical specimens. ESA immunoreactivities were usually present in the basolateral membrane of endocervical cells in the normal endocervix. However, the expressions of ESA were increasing from the basolateral membrane to the diffuse cytoplasmic membrane, along with the malignant transformation of the endocervical cells, in 6 of 11 cases with glandular dysplasia, in 9 of 9 cases with in situ and microinvasive adenocarcinomas, and in 11 of 11 cases with invasive adenocarcinomas. This finding indicates that ESA is a useful marker for endocervical glandular dysplasia and related lesions with malignant transformation, and suggests that endocervical glandular dysplasia may be a precursor lesion to uterine cervical adenocarcinomas.