Oncologic emergencies are not everyday occurrences in the ED, even at tertiary care centers. Yet, because of the growing number of patients in cancer treatment, those with problems related to their disease and its treatment will inevitably present to EDs. Since patients with cancer are at higher risk for significant morbidity and mortality at baseline, the potentially catastrophic complications of malignancy can quickly turn lethal. Therefore, it is essential for the emergency clinician to recognize these infrequent presentations and be prepared to treat them. This issue of Emergency Medicine Practice provides a review of 3 important cancer-related complications: malignant epidural spinal cord compression, superior vena cava syndrome, and malignant pericardial effusion and tamponade. The March 2010 issue of Emergency Medicine Practice, Oncologic Emergencies Part II, will address the topics of neutropenic fever, tumor lysis syndrome, and hypercalcemia of malignancy.