Mature cystic ovarian teratomas are the most common benign ovarian tumors. For their diagnosis, the following ultrasound (US) images can be considered as pathognomonic:• A cystic lesion (unilocular, very frequent, or multiple, with a densely echogenic tubercle (Rokitansky nodule).• A diffuse or partially echogenic mass with the echogenic area usually demonstrating sound attenuation.• The 'iceberg' sign, very similar to the 'sound attenuation' sign.• Fluid-fluid/fat-fluid level. Fluid-fluid levels, or fat-fluid interface, result from sebum floating above aqueous, which appears more echogenic than the sebum layer.• Dermoid mesh with hyperechoic calcifications indicating the presence of bone, teeth, or other ectodermal derivate.• Multiple mobile spherical structures (fat balls).