The aim of the study was to assess the depth of myometrial invasion by endometrial cancer using preoperative 5-9 MHz, high frequency transvaginal ultrasonography as compared with postoperative assessment using histopathologic examination. The study included 120 patients with histologically proven cancers of the endometrium. All patients underwent transvaginal sonography before surgery. The depth of myometrial invasion was classified as none, inner half of uterine wall, and outer half of uterine wall. Of 106 (88.3%) patients with proven myometrial invasion, 98 cases (92.5%) were revealed by sonography. In 109 cases (90.8%) invasion was believed to be present on transvaginal sonography. Histologically proven invasion that correlated with sonography was shown in 88 patients (73.3%). In 32 patients (26.7%) ultrasonography could not correctly predict the depth of myometrial invasion. The depth of invasion was underestimated in 10 (8.3%) cases and overestimated in 22 (18.3%) cases. Preoperative assessment of invasion of the uterine wall by transvaginal ultrasonography had an accuracy of 73% if correlated with the definitive histopathologic examination. The role of high frequency transvaginal ultrasonography in preoperative assessment of the depth of myometrial invasion in patients with endometrial cancer is limited.