We here report a case of diabetic ketoacidosis at onset of type 1 diabetes after a prolonged period of starvation due to anorexia nervosa. A 53-year-old female with a history of anorexia nervosa was admitted to the psychiatric clinic due to psychotic behaviour and inability to take care of herself. Twenty-four hours after admission she was transferred to the clinic of internal medicine due to altered mental status, and laboratory screening revealed a pH of 6.895 and blood glucose concentration of 40 mmol/L. Due to the unusual combination of prolonged starvation and diabetic ketoacidosis we implemented some modifications of existing treatment guidelines and some special considerations regarding nutrition in order to prevent a re-feeding syndrome.