Patients with hematologic malignancies are at high risk for hyperglycemia due to factors such as frequent exposure to glucocorticoids, immunosuppressants, total parenteral nutrition, and medical stress. Hyperglycemia in these patients has been associated with poor outcomes including increased risk of infection, organ dysfunction, durability of remission, graft-versus-host disease, and mortality. However, the appropriate glucose targets are not well established, and there are few prospective data assessing whether glucose control improves outcomes. HbA1c should be interpreted with caution in patients with hematologic malignancies, due to inaccuracies imposed by disordered hematopoiesis and frequent transfusions, and short-term perturbations imposed by acute illness or medications. Management of diabetes or glucocorticoid-induced hyperglycemia in the hospital generally requires insulin therapy, which is tailored based upon nutritional needs, baseline glucose control, and concomitant factors such as type and dose of glucocorticoid administration. Close follow-up and adjustment of therapy, ideally with the assistance of patient self-titration algorithms, is required after discharge. Patients are at increased long-term risk for developing diabetes and therefore should undergo regular screening.