The prognosis of endometrial endometrioid adenocarcinoma is determined in part by stage; endocervical stromal involvement (stage IIB) imparts a worsened prognosis. We describe a deceptive pattern of stage IIB disease that mimics a primary endocervical glandular proliferation and may lead to understaging of endometrial endometrioid adenocarcinoma. Fifteen cases of endometrial endometrioid adenocarcinoma with a peculiar pattern of cervical involvement were identified from our consultation files. All cases were referred in consultation because of doubt about the nature of the cervical process and its relation to the corpus tumor; in a few instances, the cervical proliferation was considered possibly benign and in one case was misinterpreted as mesonephric hyperplasia. The patients ranged from 49 to 84 years in age (mean age 64.9 years). There was usually a grossly evident endometrial tumor. The cervix was unremarkable grossly in at least 11 patients. The cervical tumors were composed of variably shaped, often tubular glands with little or no stromal response and mainly invaded as widely spaced glands that often appeared deceptively benign. In 14 cases luminal secretions, mainly eosinophilic, were identified, often leading to consideration of a mesonephric lesion. Ten of the endometrial tumors were grade 1, four grade 2, and one grade 3. One was noninvasive, nine superficially invasive, and five deeply invasive. In four cases myoinvasion had, at least in part, a diffusely infiltrative pattern. The tumors in the cervix showed no in situ component and no definite surface involvement. Continuity with the corpus tumor could be demonstrated in 12 cases. Ten of the cervical tumors invaded more deeply than the endometrial tumor, four invaded to a similar depth, and only one was more superficial than its endometrial counterpart. The cervical and corpus tumors had a similar immunoprofile in nine cases: all were vimentin positive, eight estrogen positive and one negative, four carcinoembryonic antigen negative, and five with focal apical or rare cytoplasmic staining. This immunoprofile in conjunction with routine morphologic similarity between the two tumors and the usual documented continuity between them indicate that the cervical process represents spread from the endometrial endometrioid adenocarcinoma. It is important for both therapeutic and prognostic reasons that the cervical abnormality is not misinterpreted as a benign or malignant primary endocervical glandular process.