A 66-year-old man had undergone multiple treatments for metastatic renal cell carcinoma, including 11 cycles of nivolumab, which was discontinued because of disease progression. About three weeks after discontinuing nivolumab, he reported suffering from worsening of dyspnea. Pulse oximetry showed no desaturation. His cardiovascular and pulmonary functions were normal. His dyspnea slowly worsened with no underlying diagnosis. Two months after symptoms developed, he was diagnosed with isolated adrenocorticotropic hormone deficiency. His dyspnea disappeared soon after receiving hydrocortisone. Nivolumab-induced isolated adrenocorticotropic hormone deficiency may not present with typical symptoms, and can occur even after discontinuing nivolumab. Cortisol levels should be routinely monitored in patients who receive nivolumab.