Poor dietary intake, prolonged fasting, malnutrition, alcoholism, and protein-based diets may induce ketoacidosis without diabetes mellitus. This is called "starvation ketoacidosis." Here we present the case of a patient diagnosed with starvation ketoacidosis. A 38-year-old female was admitted to our emergency department because of chest and back pain. Electrocardiography and chest X-ray showed no abnormalities. On taking her past medical history, we learned that she had been diagnosed with anorexia nervosa. Anion gap metabolic acidosis with ketone bodies in urine was detected. A diagnosis of starvation ketoacidosis was considered for the patient, and she was treated with dextrose solution for 15 h, and improved acidosis was observed. To the best of our knowledge, there are few case reports on starvation ketoacidosis. Emergency physicians should be aware of the complications of starvation and should immediately start the appropriate treatment.