Six uterine adenocarcinomas, one cervical and five endometrial, that simulated microglandular hyperplasia histologically are described. The cervical neoplasm occurred in a 34-year-old woman who had been taking oral contraceptives. The five endometrial cancers occurred in postmenopausal patients 57 to 69 years of age; two of them were receiving, or had been receiving, premarin and provera and two were receiving only premarin. The patient with the cervical neoplasm had an abnormality observed on pelvic examination. The five postmenopausal patients presented because of vaginal spotting, bleeding, or discharge; their carcinomas were discovered in endometrial curettage specimens. On initial pathologic examination two specimens were misinterpreted as benign and in the remaining four cases there was uncertainty as to whether the lesion was benign or malignant. All the neoplasms had conspicuous microglandular patterns, with the gland lumens typically containing eosinophilic mucinous secretion and numerous acute inflammatory cells, which were also characteristically prominent in the stroma. Subsequent hysterectomies in all the cases showed residual adenocarcinoma with more typical features. Three of the endometrial tumors were mucinous adenocarcinomas and two mixed mucinous and endometrioid adenocarcinomas; the cervical tumor was a moderately differentiated adenocarcinoma of endocervical type. These cases illustrate that microglandular hyperplasia should be diagnosed with caution in a postmenopausal patient, particularly if lesional tissue is present in an endometrial curettage specimen, and, rarely, cervical adenocarcinomas have foci that simulate microglandular hyperplasia.