Acute leukemias are aggressive life-threatening malignancies of the bone marrow characterized by rapid disease progression and high and early mortality. Over the past decade, advancements in antileukemic therapy coupled with improvements in early recognition and management of complications, have contributed to better clinical outcomes and survival. Nevertheless, patients remain at risk for a range of acute, and potentially fatal, complications that may arise from either the disease itself or as a consequence of antileukemic treatment. The most critical complications include tumor lysis syndrome (TLS), hyperleukocytosis with or without leukostasis, disseminated intravascular coagulation (DIC), diffuse alveolar hemorrhage (DAH), differentiation syndrome (DS), and neutropenic fever. Because each of these carries substantial morbidity and mortality, it is essential that intensivists maintain a high index of suspicion, understand the underlying pathophysiology, recognize early signs and symptoms, and initiate prompt evidence-based management. Optimal outcomes require a multidisciplinary approach, coordination with hematology/oncology, and timely escalation of care to the intensive care setting, if required.