Ultrasound is the most appropriate first imaging test to perform when gynecologic pathology is suspected based on clinical history or physical examination, and imaging is required. However, as a practical matter, a woman's first imaging test evaluating her pelvis may be a computed tomographic (CT) scan; this is especially true when these women present to an acute care facility or emergency department with chronic or acute lower abdominal pain. Radiologists need to be able to recognize the CT features of a variety of gynecologic conditions. However, just as importantly, radiologists should have a firm understanding of general principles that help to clarify when reimaging the pelvis with ultrasound is indicated; furthermore, a clear understanding of these principles helps to focus the sonologist's attention on the sonographic features that will be most helpful in further characterization of abnormal CT findings. This pictorial essay discusses these general principles that clarify when ultrasound is and is not helpful in reimaging the female pelvis after CT.