In 1982, a treatment protocol was instituted for the management of patients with clinical stage I adenocarcinoma of the endometrium. All pertinent historical, operative, and pathologic findings were reviewed by a multidisciplinary committee and 384 patients were prospectively assigned to either high- or low-risk categories. Patients were excluded from the study if they had clinically apparent extrauterine disease, clear cell or serous histologies, or microscopic ovarian metastasis. Patients were considered high-risk if they had one or more of the following factors: grade 3 tumor differentiation, myometrial invasion > 50% of the total wall thickness, pathologic cervical involvement, or adenosquamous histology. Two-hundred twenty-seven (59%) low-risk patients were followed without further treatment after surgery, while pelvic radiation was recommended for 157 (41%) high-risk patients. The 5-year relapse-free survival rates in the low- and high-risk groups were 95 and 81%, respectively. There were no treatment-related deaths. Severe or life threatening chronic radiotherapy complications occurred in 6 (5%) patients. Multivariate Cox analysis identified the following significant prognostic factors: grade, myometrial invasion, cervix involvement, and age. This treatment protocol represents a safe and effective method of managing patients with carcinoma of the endometrium and spares the need for radiation therapy in the low-risk patient.