OBJECTIVE: The aim of this study was to clarify the clinical significance of isolated tumor cells (ITCs) or micrometastasis (MM) in regional lymph nodes in patients with International Federation of Gynecology and Obstetrics (FIGO) stage I to II endometrial cancer. METHODS: In this study, a series of 63 patients with FIGO stage I to II were included, who had at least one of the following risk factors for recurrence: G3 endometrioid/serous/clear cell adenocarcinomas, deep myometrial invasion, cervical involvement, lympho-vascular space invasion, and positive peritoneal cytology. These cases were classified as intermediate-risk endometrial cancer. Ultrastaging by multiple slicing, staining with hematoxylin and eosin and cytokeratin, and microscopic examination was performed on regional lymph nodes that had been diagnosed as negative for metastases. RESULTS: Among 61 patients in whom paraffin-embedded block was available, ITC/MM was identified in nine patients (14.8%). Deep myometrial invasion was significantly associated with ITC/MM (p=0.028). ITC/MM was an independent risk factor for extrapelvic recurrence (hazard ratio, 17.9; 95% confidence interval [CI], 1.4 to 232.2). The 8-year overall survival (OS) and recurrence-free survival (RFS) rates were more than 20% lower in the ITC/MM group than in the node-negative group (OS, 71.4% vs. 91.9%; RFS, 55.6% vs. 84.0%), which were statistically not significant (OS, p=0.074; RFS, p=0.066). Time to recurrence tended to be longer in the ITC/MM group than in the node-negative group (median, 49 months vs. 16.5 months; p=0.080). CONCLUSIONS: It remains unclear whether ITC/MM have an adverse influence on prognosis of intermediate-risk endometrial cancer. A multicenter cooperative study is needed to clarify the clinical significance of ITC/MM.