A myriad of pathologies can affect the retroperitoneum in neonates. Aside from the kidneys, these pathologies majorly arise from or are related to the adrenal glands. These include congenital, metabolic, traumatic, vascular, and neoplastic etiologies. They can have a highly variable clinical presentation including asymptomatic incidental findings on abdominal imaging, upper abdominal mass detected on prenatal imaging, multiple systemic metastases from malignancy, and neonatal hypovolemic shock. Ultrasound (US) is an ideal modality to image the adrenal glands in neonates as it allows high-resolution visualization of these organs without the need for sedation or anesthesia and can be performed easily at the patient’s bedside. Ultrasound is often the initial imaging modality used to identify and diagnose neonatal adrenal pathologies. In this chapter, we review the US appearances of normal neonatal adrenal glands as well as the role of the US in diagnosing various neonatal adrenal pathologies and their mimics. Thrombosis of the major retroperitoneal vessels and rare primary retroperitoneal masses in the neonatal age group are also discussed.