Patients with leukemia, lymphoma, or multiple myeloma are prone to critical illness because of the diffuse nature of their disease and the disruption of protective mechanisms. Despite high morbidity rates, a number of these patients have an excellent probability of long-term remission if supported through a crisis. Complications that can be critical illness can be categorized as related to disease or those caused by therapy. Those with unique features or management strategies for the hematologic malignancy patient and are included in this discussion include: leukostasis, disseminated intravascular coagulation, tumor lysis syndrome, respiratory failure, and typhlitis, A case study of an acutely ill, newly diagnosed patient with several of these oncologic emergencies is used to exemplify typical clinical findings and management strategies.