In recent years, the incidence of carcinoma of the endometrium has shown an upward trend, such that it is currently the most frequently encountered malignant tumor of the female genital tract. An accurate preoperative diagnosis of the extent and spread of such carcinomas is of crucial importance for the selection of a therapeutic approach appropriate to the stage and infiltration of each particular tumor. In a prospective study of 80 patients with a carcinoma of the endometrium, performed at the Department of Obstetrics and Gynecology of the University of Mainz, we compared the preoperative findings of transvaginal sonography with the postoperative histological results with respect to the following parameters: endometrial thickness, demarcation of the boundary of the endometrium, myometrial infiltration depth and staging. In all of these patients, sonography revealed a distinct increase in the thickness of the endometrium. In all cases, the structure of the endometrium was found to be heterogenous, with an irregular and poorly delineated boundary. Assessments of the depth of tumor infiltration and the tumor staging obtained by transvaginal sonography were found to correlate with the histological findings in 85% and 87.5% of the cases, respectively. Thus, in cases of endometrial carcinoma, transvaginal sonography has an essential role to play in devising an individualized operative treatment program that takes into account the extent, spread and stage of the tumor.