In pediatric oncology patients, hemorrhagic cystitis may be a life-threatening complication of bone-marrow transplantation, chemotherapy, and/or radiation therapy. The inciting agent in urine can affect the entire urothelium from the renal collecting system to the bladder, and the severity of disease can vary. The radiologist often plays a key role in the diagnosis, follow-up, and occasionally the treatment of hemorrhagic cystitis and its complications. This review discusses the imaging findings in the kidneys and bladder in patients with hemorrhagic cystitis both before and after treatment for this disease. Findings on two-dimensional sonography, color Doppler and power Doppler sonography, computed tomography, magnetic resonance imaging, antegrade pyleography, and cystography are presented.