Objective To determine the occult coexistence of endometrial carcinoma in patients with atypical endometrial hyperplasia and to compare histological prognostic factors according to lymph node status in occult endometrial carcinoma.

Materials and Methods Two hundred and four patients from two referral centers (during the period 1990–2003) who were operated on within 1 month of endometrial biopsy for symptomatic endometrial hyperplasia without receiving any medical treatment were included retrospectively. Patients having preoperative endometrial biopsy results of concomitant endometrial hyperplasia and carcinoma were excluded from the study. Fifty-six patients having atypia in preoperative biopsy (group I) were compared with 148 patients without atypia (group II). Chi-square and Mann–Whitney U-tests were used for statistical analyses.

Results No significant difference was observed between the two groups according to age or menopausal status. Patients in group II had significantly higher parity than patients in group I. In group I, 62.5% of the patients had endometrial carcinoma, 21.4% had endometrial hyperplasia, and 16.1% had normal endometrium in hysterectomy specimens. In group II, the percentages were 5.4, 38.5, and 56.1%, respectively. Complete surgical staging was performed in 20 patients. Four patients had metastatic lymph nodes. All of them had grade 2 tumors with lymphovascular space involvement. Three of them had nonendometrioid tumors.

Conclusion Careful intraoperative and preoperative evaluation of the endometrium must be the sine qua non for patients with atypical endometrial hyperplasia. It is reasonable to do frozen section at the time of hysterectomy for atypical endometrial hyperplasia, and if grade 2/3 of nonendometriod cancer with lymphovascular space involvement is found, complete surgical staging should be performed.