Various factors associated with pelvic lymph node metastasis were analysed in 393 cases with stage I endometrial cancer treated with extended total hysterectomy, bilateral salpingo-oophorectomy and pelvic lymphadenectomy. The results are as follows. 1. The positive rates for lymph node metastasis and the relapse rate in 393 cases were 8.4% and 12.5%, respectively. 2. Myometrial invasion, tumor size, vessel permeation, cervical involvement, peritoneal cytology and adnexal metastasis were significant factors for lymph node metastasis. 3. Internal iliac nodes were the most common metastatic sites for cases with a single node metastasis, whereas external iliac nodes were the most common in all cases with lymph node metastasis. 4. The relapse rate for cases with single node metastasis was 40%, while the relapse rate for cases with three or more metastatic lymph nodes was 70%. 5. The relapse rate for 33 cases with lymph node metastasis was 54.5% and all of the relapse cases showed distant recurrence, whereas the relapse rate for 360 cases without lymph node metastasis was only 8.6%. It is therefore considered that pelvic lymphadenectomy is important in detecting high-risk patients and to reduce the relapse rate. Cytotoxic chemotherapy seems to be more adequate as adjuvant therapy for cases with lymph node metastasis.