Refeeding syndrome (RS) is one of the serious complications during treatment of anorexia nervosa. It includes hormonal and metabolic changes that occur during the process of refeeding in chronically malnourished patient when nutrition is introduced in an excessive and improper amount. RS manifests in water-electrolyte imbalances, including hypophosphatemia (the mostimportant diagnosticmarker), hypokalemia, hyponatremia, hypomagnesaemia, fluid retention, vitamin deficiency and metabolic acidosis. It applies to either oral and parenteral supplementation. In the treatment of malnourished patients with anorexia nervosa, it is essential to establish an initial caloric amount that will stimulate weight gain from the beginning of treatment, increase its effectiveness while minimizing the risk of RS. Recent research suggests that the current recommendations may be too stringent in this respect and require further updating. Awareness of the risks associated with RS, including significant mortality, appears to be currently insufficient also among physicians. There is a need for far more specialized multidisciplinary centers for patients with anorexia nervosa and also appropriate algorithms and standards of care for that population. The aim of this paper is to systematize the current knowledge about RS and RS prevention, to increase awareness of its occurrence and present the results of the latest research on safe resupplementation of patients suffering from anorexia nervosa.