A retrospective analysis is reported in 858 patients with clinical Stage I carcinoma of the endometrium treated definitively with combined irradiation and total abdominal hysterectomy and bilateral salpingo-oophorectomy (TAH-BSO) from January 1960 through December 1986. Most patients received a preoperative intracavitary insertion (3500-4000 mgh to the uterus and a 6500 cGy surface dose to the upper vagina) followed by a TAH-BSO within 1-2 weeks. Some patients received postoperative external beam irradiation (2000 cGy whole pelvis and an additional 3000 cGy to the parametria, with a midline stepwedge) when factors such as deep myometrial invasion were present. Occasionally patients were treated with a preoperative intracavitary insertion and preoperative external beam irradiation (2000 cGy whole pelvis). The 5-year progression-free survivals by FIGO (1988) surgical stage were 93% for IA, 90% for IB, and 91% for Stage IC. An analysis of multiple variables was performed to ascertain their prognostic significance. Factors that significantly affected the 5-year progression-free survivals by univariate analysis were grade (grade 1 = 95%, grade 2 = 88%, grade 3 = 73%; p less than 0.0001), histology (adenoacanthoma = 96%, clear cell = 89%, adenocarcinoma = 89%, papillary = 81%, adenosquamous = 80%; p = 0.04), lower uterine segment involvement (uninvolved = 89%, involved = 73%; p = 0.006), depth of myometrial invasion (no residual tumor = 91%, limited to the endometrium = 96%, less than 1/3 myometrial penetration = 92%, 1/3 - 2/3 = 100%, greater than 2/3 = 50%; p = 0.02), peritoneal cytology (negative = 92%, positive = 56%, p less than 0.0001), uterine serosal involvement (uninvolved = 89%, involved = 55%; p less than 0.0001), vascular space invasion (absent = 89%, present = 75%; p = 0.001), and the presence of extrauterine disease (absent = 90%, present = 64%; p less than 0.0001). A multivariate analysis of these prognostic variables showed that histological grade (p = 0.001), peritoneal cytology (p = 0.004), and uterine serosal involvement were prognostic for local failure and that peritoneal cytology (p less than 0.001), grade (p = 0.001), age (p = 0.002), and extrauterine disease (p = 0.02) were prognostic for the development of distant metastasis.