Adrenal insufficiency is an uncommon cause of hypercalcemia and not easily considered as an etiology of adrenal insufficiency in clinical practice, as not all cases of adrenal insufficiency manifest as hypercalcemia. We report a case of secondary adrenal insufficiency presenting as hypercalcemia and acute kidney injury in a 66-year-old female. The patient was admitted to the emergency department with general weakness and poor oral intake. Hypercalcemia (11.5 mg/dL) and moderate renal dysfunction (serum creatinine 4.9 mg/dL) were shown in her initial laboratory findings. Studies for malignancy and hyperparathyroidism showed negative results. Basal cortisol and adrenocorticotropic hormone levels and adrenocorticotropic hormone stimulation test confirmed the diagnosis of adrenal insufficiency. With the administration of oral hydrocortisone, hypercalcemia was dramatically resolved within 3 days. This case shows that adrenal insufficiency may manifest as hypercalcemia and acute kidney injury, which implicates that adrenal insufficiency should be considered a cause of hypercalcemia in clinical practice.