The purpose of this study was to quantify vascular density in the stroma of normal, hyperplastic, and neoplastic endometria and to explore its relationship to other prognostic features of endometrioid adenocarcinoma. Curettage specimens of proliferative and mid-secretory endometrium; simple, complex, and atypical endometrial hyperplasia; and grade I endometrioid adenocarcinoma were stained with Factor VIII-related antigen. The number of vessels per mm2 of stroma was calculated for each case. The stroma of mid-secretory and hyperplastic endometrium was more vascular than that of proliferative endometrium. The stroma of adenocarcinoma, though reduced in proportion to the epithelium, was significantly more vascular than that of normal or hyperplastic endometrium. Stromal vascular density was not related to the depth of invasion, the presence of lymphovascular space permeation, or the state of the adjacent endometrium, whether atrophic or hyperplastic.