From December 1980 to February 1991 24 patients with endometrial hyperplasia after estrogen treatment were followed-up at the Department of Obstetrics and Gynecology, University Hospital, Lund, Sweden. All were referred for post-menopausal bleeding. They were followed-up with abrasio three and nine months after the initial diagnosis. Seven patients demonstrated cystic glandular hyperplasia (CGH), six adenomatous hyperplasia (AD) and eleven atypical hyperplasia (AT). In the CGH-group five revealed atrophic endometria and one developed into endometrial carcinoma. In the AD-group two patients refused follow-up, four had atrophic endometria, in the AT-group five developed atrophia, one refused follow-up, one developed CGH, while three developed carcinoma. All four carcinomas in the series developed within the first three months of follow-up. The frequency of carcinomatous development was much higher for exogen estrogen induced hyperplasias compared to earlier findings for endogenously estrogen-induced endometrial hyperplasias. It is recommended that non-opposed estrogen treatment should be used in rare circumstances under close follow-up and that patients developing endometrial hyperplasias are followed-up until the hyperplastic changes have disappeared.