From 1973 to 1987, 16 patients with International Federation of Gynecology and Obstetrics (FIGO) Stage I serous papillary endometrial carcinoma were evaluated and treated at the University of Kentucky Medical Center (Lexington, KY). All patients were 60 years of age or older, and all were postmenopausal. Patients were treated with total abdominal hysterectomy, bilateral salpingo-oophorectomy, and paraaortic lymph node sampling, and 38% were noted to have more extensive disease than appreciated clinically. Nine patients were given adjuvant postoperative radiation. Seven patients (44%) developed recurrent cancer with liver, lung, and upper abdomen being the most common sites of spread. Prognosis was most directly related to the presence of lymph vascular space invasion and the depth of myometrial penetration. No patient with serous papillary carcinoma confined to the endometrium developed recurrent cancer. In contrast, the recurrence rate of patients having myometrial invasion was 70% (P less than 0.03). Hormonal therapy was of limited value in the treatment of recurrent disease. This data suggests the need for adjuvant systemic therapy in the treatment of patients with Stage I serous papillary carcinoma of the endometrium who have myometrial invasion.