Children with cancer are at increased risk of life-threatening emergencies, either from the cancer itself or related to the cancer treatment. These conditions need to be assessed and treated as early as possible to minimize morbidity and mortality. Cardiothoracic emergencies encompass a variety of pathologies, including pericardial effusion and cardiac tamponade, massive hemoptysis, superior vena cava syndrome, pulmonary embolism, and pneumonia. Abdominal emergencies include bowel obstruction, intussusception, perforation, tumor rupture, intestinal graftversus-host disease, acute pancreatitis, neutropenic colitis, and obstructive uropathy. Radiology plays a vital role in the diagnosis of these emergencies. We here review the clinical features and imaging in pediatric patients with oncologic emergencies, including a review of recently published studies. Key radiological images are presented to highlight the radiological approach to diagnosis. Pediatricians, pediatric surgeons, and pediatric radiologists need to work together to arrive at the correct diagnosis and to ensure prompt and appropriate treatment strategies.