Bone marrow transplantation is a complex therapy designed as curative for a variety of malignant and nonmalignant diseases. It is a highly invasive procedure that uses high-dose chemotherapy and may also include radiation treatment. This results in immunosuppression that is often followed by infection, graft-vs-host disease, pulmonary complications, veno-occlusive disease of the liver, and metabolic and nutritional abnormalities. Parenteral nutrition has been the mainstay of nutrition support in patients undergoing bone marrow transplantation. Parenteral nutrition has not been uniformly successful in improving nutritional status or outcome. Enteral nutrition offers many theoretical advantages but is often not well tolerated. Coordinated efforts of the health care team are needed to optimize the nutrition support of these complicated cases.