The myometrial invasion depth of endometrial cancer is an important prognostic factor. The preoperative assessment is decisive for the appropriate surgical treatment. In 96 patients with endometrial cancer, the myometrial invasion depth (greater than 50% or less than 50%) was measured preoperatively using transvaginal sonography (TVS). The sonographic results were compared to the histopathological findings. A sensitivity of 93% was obtained for invasion depths greater than 50%. The predictive value of an invasion depth less than 50% was 93% as well. In 16% of the cases the invasion depth was overestimated while, in only 3% it was underestimated. The diagnostic accuracy was 81%. Forty-five patients were examined preceding a diagnostic dilatation and curettage and fifty-one were examined following a diagnostic dilatation and curettage. The diagnostic accuracy in both groups was equivalent. Using transvaginal sonography, the spread of cancer to the cervix was observed in five of the seven cases in which it was postoperatively confirmed. TVS is a valuable, non-invasive diagnostic method for patients with endometrial cancer. When the TVS data are combined with results from other preoperative tests, the prognostic information obtained provides a useful basis in choosing the appropriate therapy.