Bone marrow transplantation is often associated with multiple organ failure which is usually reversible. Oral mucositis and dysphagia, vomiting, diarrhoea, protein losing enteropathy, transient exocrine pancreatic impairment, hypoalbuminaemia, biochemical trace element and mineral de®ciencies are all common following transplantation and have profound nutritional consequences. Malnutrition affects negatively the clinical outcome. Nutritional support is provided to malnourished patients and those who suffer deterioration in nutritional status despite the provision of dietetic counselling. Only a few randomised studies comparing enteral with parenteral nutrition after transplant exist. Both enteral tube feeding (in the absence of mucositis) and parenteral nutrition are effective in maintaining nutritional status. However, enteral nutrition is associated with a better nutritional response and fewer complications than parenteral. With existing enteral and parenteral nutrition regimens close monitoring of trace element and mineral status is required.