Refeeding syndrome (RFS) is the result of aggressive enteral or parenteral feeding in a malnourished patient, with hypophosphatemia being the hallmark of this phenomenon. Other metabolic abnormalities, such as hypokalemia and hypomagnesemia, may also occur, along with sodium and fluid retention. The metabolic changes that occur in RFS can be severe enough to cause cardiorespiratory failure and death. This article reviews the pathophysiology, the clinical manifestations, and the management of RFS. The key to prevention is identifying patients at risk and being aware of the potential complications involved in rapidly reintroducing feeds to a malnourished patient.