A prospective study was designed to determine the sensitivity and specificity of nonenhanced T2-weighted and contrast material-enhanced T1-weighted magnetic resonance (MR) imaging in assessing the depth of myometrial invasion in patients with proved endometrial cancer. In 56 consecutive patients with clinically determined early-stage disease, findings of the two MR imaging techniques were compared with results of histologic examination of surgical specimens. Myometrial invasion was classified as absent (stage IA), superficial (stage IB), or deep (stage IC). In the assessment of each tumor stage, the sensitivity and specificity of contrast-enhanced T1-weighted MR imaging were higher than those of non-enhanced T2-weighted MR imaging. In determining the degree of myometrial tumor invasion, the overall sensitivity of enhanced T1-weighted MR imaging was 87.5%, whereas that of nonenhanced T2-weighted MR imaging was 71.4% (P less than .05). The use of contrast material may improve the ability to assess, with MR imaging, the depth of myometrial invasion by endometrial cancer.