PURPOSE: The purpose of this study is to present imaging findings of MMMT developed after irradiation and to compare them with those not associated with irradiation. MATERIALS AND METHODS: Patients with pathologically-proven MMMT were divided into two groups ; group 1, with a history of pelvic irradiation (n=9), and group 2, without such history(n=4). With regard to tumor location, size, extent, degree of myometrial invasion, presence of enhancement, and internal texture of a tumor, we analyzed CT(n=10) and MR imaging (n=8) findings in each group. RESULTS: The tumor was larger in group 1 (average 8.7 cm) than in group 2 (average 5.5 cm). In eight patients in group 1, the endometrial cavity was distended, with remarkable fluid retention, and a mass was found in the fundus or body. The junctional zone was disrupted and hemorrhagic or necrotic foci were found within the mass. In all patients in group 2 and in one in group 1, a tumor had replaced the endometrial cavity, without fluid retention. CONCLUSION: Imaging findings of irradiation-associated MMMT appeared to be different from those not associated with irradiation. Where there are findings of a distended endometrial cavity filled with fluid andmural mass, one should be alert to the possibility of irradiation-associated MMMT.