Adrenal insufficiency (AI) is the inadequate production of adrenocortical hormones: glucocorticoids, mineralocorticoids, and adrenal androgens. Primary AI, also called Addison’s disease, is caused by adrenal gland disorder (autoimmune disease, infections, and malignancy, among others). Adrenal insufficiency can also occur because of decreased production of adrenocorticotropic hormone (ACTH) from disease in the pituitary gland (secondary) or hypothalamic disorders and prolonged glucocorticoid therapy (tertiary). Diagnosis is by demonstrating hypocortisolism (via cortisol and ACTH levels and ACTH-stimulation test) and determining the etiology (adrenal autoantibodies, imaging). Glucocorticoid replacement is needed in all forms of AI. Additionally, in primary AI, mineralocorticoid is given to prevent volume depletion, salt loss, and hyperkalemia. Adrenal crisis is a medical emergency; management requires prompt IV hydration and administration of IV glucocorticoids without waiting for initial hormone results.