Urinary bladder masses are rare in children, and the associated histologic features and prognoses in this population are different from those in adults. Most children with urinary bladder masses present with lower urinary tract symptoms, which may include hematuria, dysuria, frequent urination, and urgency to urinate. However, some of these masses may be identified incidentally or involve generic symptoms such as abdominal distention. In general, pediatric bladder tumors can be divided into those that originate from the bladder epithelium, known as urothelial neoplasms, and mesenchymal bladder neoplasms, which are more prevalent. The most common bladder malignancy in children is a rhabdomyosarcoma, whereas the most common benign bladder lesion in the pediatric population is a papillary urothelial neoplasm of low malignant potential (PUNLMP). The first-line imaging tool for assessing bladder lesions is ultrasonography, which may be followed by a cross-sectional imaging examination such as computed tomography or magnetic resonance imaging if the origin of the mass is unclear or if distant spread is suspected. Although imaging may enable the radiologist to suggest a differential diagnosis based on lesion location and patient age, tissue biopsy generally is required to identify the exact pathologic entity. This is usually performed at cystoscopy and may be curative in cases in which the lesion is small and has low recurrence potential. Knowledge of the clinical, histopathologic, and imaging features of common bladder neoplasms is essential, as it can aid in preventing imaging pitfalls. These may include the misinterpretation of either a pelvic mass as arising from the bladder or a bladder mass as arising from the pelvis, and interpreting an inflammatory mass or bladder detritus as a neoplasm. ©RSNA, 2017.