A 33-year-old woman was incidentally found to have a polypoid adenofibroma on MR imaging during the evaluation of carcinoma in situ of the cervix. The position of the polypoid lesion was variable from time to time. Although the lesion was a benign pedunculated one, T2-weighted MR images showed disruption of "junctional zone" in the posterior myometrial wall of the uterus, mimicking myometrial invasion of endometrial carcinoma.