The pathologic features of a prospective study of FIGO stage I endometrial cancer is presented. The uterus, tubes, ovaries, and pelvic lymph nodes of 222 cases and aortic nodes of 157 cases have been analyzed. The surgical-pathologic specimen would suggest a negligible risk for lymph node metastasis if: cancer is confined to the endometrium irrespective of grade, invasion is superficial for grades 1 and 2 tumor, the intermediate third of the myometrium is invaded for grade 1 tumor only, and occult disease is not present in the cervix and/or adnexa. Conversely, a substantial risk for lymph node metastasis exists if the surgical-pathologic study identifies superficial myometrial invasion by grade 3 cancer, intermediate myometrial invasion by grade 2 or 3 cancer, deep myometrial invasion by cancer of any grade, vascular space involvement, and extension of tumor to the cervix and/or adnexa.