The purpose of the study was to evaluate certain histological features of adenomatous hyperplasia diagnosed in endometrial curretings, that will enable us to distinguish atypical glandular hyperplasia from early well-differentiated adenocarcinoma. The material for this study was composed of 519 endometrial hyperplasias diagnosed in curettings. Of these, 244 were adenomatous hyperplasias, 109 were cystic hyperplasias, 93 mixed types and 73 were atypical hyperplasias. The cases of atypical hyperplasia were subsequently operated on, and among them, 26 proved to be adenocarcinomas. All histological sections of the currettings showing the atypical hyperplasia were re-evaluated to find criteria diagnostic of adenocarcinoma. The authors have considered as diagnostic criteria the stroma infiltration, the mitotic activity, the nuclear atypia, the stratification of nuclei and the presence of necrosis. The stroma infiltration seems to be the most important indication of an adenocarcinoma of the endometrium.