A multicenter trial on apparent stage I endometrial carcinoma was performed to establish an intensive surgical staging, to formulate a treatment on the basis of the pathological extent of the disease and to determine the effectiveness of adjuvant medroxyprogesterone acetate therapy. The results of the first objective on 1,055 patients are herein reported. All patients had total abdominal hysterectomy, bilateral salpingo-oophorectomy, colpectomy of the superior third, and biopsy of lymph nodes positive or doubtful at radiological imaging or on surgical inspection. On the basis of the pathologic extent of the disease, patients were classified into five categories: disease outside the uterine corpus (RE); disease limited to endometrium (RO); disease with inner myometrial invasion and high or moderate grade (R1); disease with deep myometrial invasion or poor differentiation (R2); disease with positive retroperitoneal nodes (R3). One hundred and forty-six patients were RE, 163 RO, 382 R1, 341 R2 and 23 R3. The results showed a clinical understaging in 16% of the cases. According to the new FIGO classification, the relapse-free survival at 84 months was 96% for patients at stage IA, 92% for patients with stage IB-C, 86% for stage IIA-B, 76% for stage IIIA-B and 74% for patients at stage IIIC. These data confirm the importance of an intensive surgical staging in apparent stage I endometrial carcinoma.