OBJECTIVES: To describe the clinical history and ultrasound findings in patients with ovarian dysgerminoma. METHODS: This was a retrospective study of patients with a histological diagnosis of ovarian dysgerminoma who had undergone preoperative ultrasound examination. The patients were identified from the databases of 11 ultrasound centers. The tumors were described by the principal investigator at each contributing center on the basis of ultrasound images, ultrasound reports and research protocols (when applicable) using the terms and definitions of the International Ovarian Tumor Analysis (IOTA) group. In addition, three authors reviewed all available electronic ultrasound images (gray-scale images and color/power Doppler images were available for 18 patients and 14 patients, respectively) and described them using subjective evaluation of gray-scale and color Doppler ultrasound findings (here called pattern recognition). RESULTS: Twenty-one patients with ovarian dysgerminoma were identified (including one woman with bilateral masses). Twenty patients had a primary ovarian dysgerminoma (including the one with bilateral masses) and one patient had a recurrence of dysgerminoma in her retained ovary. One of the 21 patients was pregnant. All tumors except one were pure dysgerminomas, one being a mixed germinal cell tumor with 30% dysgerminoma component. Median age was 20 (range, 16-31) years. Information on clinical symptoms was available for 18 patients. In four patients, the tumor was detected incidentally, whereas 14 patients presented with one or more of the following symptoms: acute pain (n = 4), chronic pain (n = 8), bloating (n = 8), menstrual disorders (n = 5) and infertility problems (n = 1). One (5%) patient had ascites. Using the IOTA terms and definitions, all but one dysgerminoma were moderately (43%) or very well (50%) vascularized solid tumors. One tumor was multilocular-solid. According to pattern recognition, most dysgerminomas were highly vascularized, purely solid tumors with heterogeneous internal echogenicity divided into several lobules, had a smooth and sometimes lobulated contour and were well-defined relative to the surrounding organs. CONCLUSION: The ultrasound finding of a highly vascularized, large, solid, lobulated adnexal mass with irregular internal echogenicity in a woman 20-30 years old should raise the suspicion of ovarian dysgerminoma.