Because pelvic ultrasound is commonly used to evaluate adnexal masses, it is important to understand the most useful sonographic features for predicting benign and malignant masses. Determining whether an adnexal mass is of ovarian or extraovarian origin is key in arriving at the most likely diagnosis. Most adnexal masses are benign, and each of the most common benign ovarian lesions has a typical sonographic appearance. Additionally, most malignant ovarian neoplasms have a solid component with detectable flow by Doppler ultrasound, allowing one to strongly suggest the diagnosis. We will review an approach to the ultrasound diagnosis of adnexal masses that progresses through a series of 4 questions to help lead one to the most likely diagnosis.