Adrenal insufficiency patients are treated with glucocorticoid replacement therapy. However, mimicking the in vivo circadian rhythm of cortisol levels is challenging, and suboptimal replacement increases the risk of mortality from cardiovascular disease. We herein report a case of coronary spastic angina (CSA) with simultaneous low early-morning serum cortisol levels in a patient undergoing corticosteroid replacement therapy for primary adrenal insufficiency. Steroid therapy is reportedly effective for refractory angina, but underlying adrenal deficiency has never been revealed. Our case intimates the probable risk of CSA as a complication of relative adrenal insufficiency and highlights the effectiveness of dexamethasone in these patients.