After completion of this article, the reader should be aware of the symptoms of BOTs, the potential role and pitfalls of tumor marker measurement. In addition, the reader will understand the appearance of BOTs at imaging techniques; the reader will be able to compare and combine ultrasonography, MRI and positron emission tomography in diagnosing BOTs. In clinical practice, the reader should be better able to assess whether an ovarian mass is a benign tumor, a BOT or an invasive cancer.