Cancer in children is the second cause of death between 5 and 9 years of age and third between 10 and 14 years of age. Approximately 15,000 children and adolescents (ages 0–19) are diagnosed with cancer annually. Survival rates for some malignancies now surpass 88%. The use of more aggressive treatment modalities to reach these results has been associated with a greater risk for severe life-threatening oncologic emergencies requiring pediatric intensive care (PICU). This chapter focuses on early recognition and treatment of some of the most common oncologic emergencies in children with cancer.