In most cases, the endometrioid adenocarcinoma of the endometrium is preceded by hyperplasia with different risk of progression into carcinoma. The original histologic slides from 560 consecutive cases with complex and atypical hyperplasia were re-examined to assess the interobserver-correlation. The hyperplasias were analyzed separately for their likelihood of progression to carcinoma in patients with and without progestogen hormonal therapy. In all cases, a fractional re-curreting was performed to establish the state of the disease. The leading symptom was vaginal bleeding in 65.5% of the cases in the postmenopausal period. Eighty-six percent of the patients presented with obesity (BMI > 30 kg/m(2)), 23% had had an exogeneous use of estrogens. Twenty-two cases were reclassified as simple hyperplasia and excluded from further analysis. The interobserver-correlation was 91% for complex, 92% for atypical hyperplasia, and 89% for endometrioid carcinoma, representing an overall correlation of 90%. Two percent of the cases with complex hyperplasia (8/390) progressed into carcinoma and 10.5% into atypical hyperplasia. Fifty-two percent of the atypical hyperplasias (58/112) progressed into carcinomas. In the case of progestogen treatment (n = 208; P < 0.0001) 61.5% showed remission confirmed by re-curetting, compared with 20.3% of the cases without hormonal treatment (n = 182; P < 0.0001). Endometrial hyperplasia without atypia is likely to respond to hormonal treatment. Especially in postmenopausal situation, atypical hyperplasia should be treated with total hysterectomy.