Magnetic resonance (MR) imaging may aid in preoperative treatment planning of endometrial carcinoma by accurately estimating tumor volume, depth of myometrial invasion, and extrauterine extension. Preoperative MR scans were obtained on 24 women with clinical stage I endometrial cancer. MR scans were evaluated for uterine size, as an indirect measure of tumor volume, and depth of myometrial invasion. MR detected deep invasion (greater than or equal to 50% of myometrial thickness) with a sensitivity of 71% and specificity of 83% (accuracy 79%) when compared with the pathologic findings. MR staging may assist in deciding which patients should have lymph node dissection at surgery and may aid in decisions regarding adjunctive radiation therapy.