We report a rare case of Addisonʼs disease due to bilateral adrenal metastasis from gastric cancer. The patient was an 85-year-old man, who had underwent distal gastrectomy and received postoperative adjuvant chemotherapy for gastric cancer. In 2009, the patient was found to have multiple metastases in the para-aortic lymph nodes and the left adrenal gland. Chemotherapy for metastatic gastric cancer was initiated; however, subsequently metastasis to the right adrenal gland was noted. In January 2012, the patient presented at our hospital with aspiration pneumonia. He was found to have general fatigue, hyponatremia, hyperkalemia, and eosinophilia. Although he seemed like cachexia at first glance, we suspected adrenal insufficiency because these abnormalities didnʼt improve with nonspecific therapy. A rapid adrenocorticotropic test was performed, and as no increase in the blood cortisol levels was demonstrated, a diagnosis of Addisonʼs disease was made. The patient improved dramatically with hydrocortisone treatment. Thus, the possible diagnosis of Addisonʼs disease must be considered and an adrenal function test should be performed for patients with bilateral adrenal metastasis.