Refeeding syndrome is an under diagnosed, but clinically important syndrome, and can be defined as acute electrolyte abnormalities, fluid retention, and dysfunction of various organ systems in malnourished patients undergoing refeeding, whether orally, enterally, or parenterally. The hallmark biochemical feature of refeeding syndrome is hypophosphatemia. The syndrome almost always develops during the early stages of refeeding. To avoid the development of this potentially lethal condition, nutritional support in patients at risk should be increased gradually over a period of several days while assuring adequate amounts of vitamins and minerals.