[en] A restrospective analysis was carried out of 17 magnetic resonance images obtained in 13 patients with histologically proven endometrial cyst. Endometrial cysts were seen as high-intensity areas on short and long spin echo and inversion recovery images. This is in sharp contrast with images of other gynecologic masses such as ovarian and uterine masses. Endometrial cysts had evidently decreased Tl when compared with other gynecologic masses. Magnetic resonance imaging proved to have a great potential in the differentiation of endometrial cysts from cystic ovarian masses and some uterus myoma that is frequently difficult on ultrasound and X-ray computed tomography. (Namekawa, K.)