The surgical pathologic features of 621 patients with Stage I carcinoma of the endometrium are presented. All patients were treated with primary surgery consisting of total abdominal hysterectomy, bilateral salpingo-oophorectomy, selective pelvic and paraaortic lymphadenectomy and peritoneal cytology. An appreciable number of patients (144-22%) with Stage I cancers have disease outside of the uterus (lymph node metastasis, adnexal disease, intraperitoneal spread and/or malignant cells in peritoneal washings). Multiple prognostic factors particularly grade and depth of invasion are related to extrauterine disease. This study adds credence to the primary surgical approach with individualized postoperative therapy as indicated.