All pelvic masses in children require a plain film of the abdomen and pelvis first, followed by US of the pelvis. Many benign or cystic abnormalities can be identified at this level of imaging. If a solid or malignant appearing abnormality is identified by US, the next examination will typically be a CT of the abdomen & pelvis with oral & IV contrast. Genitourinary congenital anomalies and sacrococcygeal teratomas will probably require MRI for further characterization. Abdominal masses in children require a slightly different approach: the main determinant becomes age. In children <5 years of age the first step is a plain film of the abdomen followed by US. Many benign entities are defined at this point. Solid masses require CT of the abdomen & pelvis with oral & IV contrast; in patients <3 years of age with a likely diagnosis of neuroblastoma MRI is the next step directly after US. In patients >5 years of age the first step is a plain film of the abdomen followed by CT of the abdomen & pelvis with oral and IV contrast; US isn't routinely a first-line modality.