Anorexia nervosa (AN) is a serious psychiatric disorder which typically occurs in young women; however, more and more cases in middle-aged women are being reported. The management of this complex disease requires a team approach, and full recovery occurs only in 50% of patients. Endocrine and metabolic complications are commonly observed, the latter of which may even be life-threatening, and require prompt and proper management. Infections, albeit reported, are not usually a major clinical problem in these patients. We herein report the case of a severely malnourished middle-aged woman with long-standing AN who was hospitalized with marked hypokalaemia (1.5 mEq/L) and rhabdomyolysis; during hospitalization she developed septic shock and acute respiratory distress syndrome, which required urgent admission to the intensive care unit. She underwent sedation and tracheal intubation for mechanical ventilation and was managed with combined therapies, which eventually led to a successful outcome. Life-threatening medical complications can occur not only in young women but in middle-aged women with AN as well and require a combined multidisciplinary approach.