Aims: To describe the ultrasound features of benign struma ovarii that often mimic ovarian cancer in the background of complex clinical and histopathological pictures. Material and methods: We retrospectively identified patients with histologically confirmed benign struma ovarii, treated in our institution between 2003-2016 with complete imaging, clinical, and histopathological data available. Ultrasound findings were drawn from images, and reports using terms and definitions of the International Ovarian Tumor Analysis group and pattern recognition description was applied. Results: In all, 19 patients were identified; 10 with pure and 9 with impure struma. Median age was 47 (range 24-69); 10 (53%) were premenopausal. Only four (21%) patients presented with pain, others were asymptomatic. Using pattern recognition, 74% strumas (14/19) were uni-/multilocular solid or solid tumors. The solid components were roundish with smooth contours. Six struma pearls were detected. The subjective color score was moderate or abundant in the majority of solid components. Only 5 (26%) tumors were purely cystic. Conclusions: The ultrasound characteristics differ widely from typical mature ovarian teratoma. Features such as, solid roundish components with smooth contours, struma pearls, acoustic shadowing and occasionally signs of dermoid are clues and may help preoperatively to differentiate benign struma from malignant adnexal lesions.