CONTEXT: Mucins are glycoproteins produced by both normal and neoplastic glandular epithelial cells including endocervix. OBJECTIVE: To determine the expression of mucins in uterine cervical glandular lesions and whether mucin expression correlates with the nature and origin of the glandular lesions. DESIGN: Antibodies to MUC1, MUC2, MUC4, and MUC5AC were applied on 52 cases including 14 endocervical adenocarcinomas (including 4 adenosquamous carcinomas), 9 endometrial carcinomas (8 endometrioid adenocarcinomas and 1 adenosquamous carcinoma), 8 adenocarcinoma in situ (AIS), 2 glandular dysplasias, 6 tubal metaplasias, 10 microglandular hyperplasias, and 3 normal endocervix. The presence of any staining was considered positive. RESULTS: All benign endocervical epithelia, including tubal metaplasia and microglandular hyperplasia, expressed MUC1, MUC4, and MUC5AC but not MUC2. Almost all endocervical AIS and carcinomas and all endometrial adenocarcinomas expressed MUC1; the exceptions were 2 cases of endocervical adenocarcinoma and 1 case of adenosquamous carcinoma of the endocervix. MUC2 staining was noted in 25%, 40%, and 22% of AIS, endocervical adenocarcinomas, and endometrial adenocarcinomas, respectively. About 38% of AIS, 75% of endocervical adenocarcinomas, and 44% of endometrial adenocarcinomas expressed MUC4. Half of AIS, most of endocervical adenocarcinomas, and 22% of endometrial adenocarcinomas expressed MUC5AC. The difference in MUC4 and MUC5AC expression between benign endocervical lesions and AIS and the difference in MUC5AC expression between endocervical and endometrial neoplasms were statistically significant. CONCLUSIONS: Mucin expressions differed among benign endocervical lesions and AIS and among endocervical and endometrial malignancies. These results suggest that mucin staining may potentially be helpful in differentiating various uterine cervical glandular lesions.