A review of the histologic material from 100 patients with endometrial carcinoma revealed 10 cases in which endocervical-type epithelium constituted an integral component of endometrial adenocarcinoma. In nine of these, the endocervical epithelium was focal while in one patient, reported in detail, the curetted endometrial carcinoma presented as an almost pure endocervical-type lesion. In most instances, the endocervical epithelium was papillary and mature, but areas of tufting, pseudostratification and atypism were also evident. Endocervical-type epithelium in endometrial cancers was more common in curettings than in hysterectomy specimens probably because of its superficial location within the tumor. The endocervical nature of these components, which are most likely of metaplastic origin, was evident on light and electron microscopy. Histochemical stains established the similarities of the cytoplasmic mucins of these cells to that of normal endocervix and well-differentiated endocervical adenocarcinoma and emphasized the dissimilarities to the mucin content of papillary, secretory and clear-cell endometrial carcinoma. Thus, awareness of this type of lesion, application of strict histologic criteria and use of histochemical stains make it possible to reach the correct diagnosis in most cases, even in those in which the endocervical-type epithelium composes the major portion of curettings from an endometrial adenocarcinoma.