Hematologic complications are common in cancer patients and often require urgent management in the intensive care setting. Cytopenias result from complex, overlapping mechanisms such as marrow infiltration, treatment-induced myelosuppression, immune dysregulation, systemic inflammation, and nutritional deficiencies, complicating diagnosis and treatment. This chapter reviews the pathophysiology, diagnosis, and management of anemia, thrombocytopenia, neutropenia, and coagulopathies in critically ill oncological patients. Anemia is explored through hypoproliferation, hemolysis, and hemorrhage, considering inflammation, chemotherapy effects, micronutrient deficiencies, and microangiopathy. Thrombocytopenia is discussed in the context of marrow suppression, immune destruction, consumptive coagulopathy, and splenic sequestration, including novel treatments like thrombopoietin receptor agonists. Neutropenia is reviewed across congenital, chemotherapy-related, and drug-induced causes, emphasizing infection risk and hematopoietic growth factors. Coagulopathies cover disseminated intravascular coagulation, thrombotic microangiopathies, acquired inhibitors, and malignancy-specific syndromes. Integrating clinical, morphological, and laboratory data is vital for effective management and optimizing outcomes in hematology-oncology critical care.