Anorexia nervosa is a physical and mental health condition with high mortality and long-term history. Its most characteristic symptom is a significant underweight caused and maintained by a patient who is perceived as an obese person and sets a low weight limit. The course of treatment is usually long-term, involving a large group of specialists, and, depending on the patient’s condition, outpatient care, day care or – in the event of high weight loss or malnutrition complications – hospitalization for several months is necessary. Currently, there is a tendency to shorten the length of stay in the inpatient ward of patients with AN in favor of other forms of care. The aim of this article is to collect and present the results of a small number of studies on factors affecting the length of hospitalization in the treatment of anorexia nervosa. Based on the currently available tests, the body mass index at admission should be considered as a factor significantly affecting the length of hospitalization. However, the discussion remains open and further research in this area is advisable. Clarification of the above issue may provide the basis for a more patient-oriented determination of the duration of hospital treatment. Further research on factors identified in individual studies and their relationships will also be needed.