Refeeding syndrome refers to a life-threatening shift of electrolytes and fluid with metabolic abnormalities in malnourished patients undergoing refeeding, whether orally, enterally, or parenterally. Clinical findings are fluid-balance abnormalities, abnormal glucose metabolism, hypophosphatemia, hypomagnesemia, hypokalemia and deficiencies of vitamin and trace element. Multiple organ systems including cardiac, respiratory, neurologic, renal, hematologic, and gastrointestinal can be affected. When recognized in a timely manner, these complications can be easily and successfully prevented and treated. Four factors appear fundamental: early identification of patients at risk, correction of abnormalities before refeeding, close monitoring during refeeding, and an appropriate feeding regimen.