A 62-year -old male patient who had undergone total extirpation of type 3 cancer of the greater curvature of the upper stomach body at another hospital received postoperative chemotherapy with 5-FU and methotrexate. The patient was subsequently treated with oral 5-FU. About 1 year later, a 4 cm tumor of the left adrenal gland was revealed by abdominal CT and diagnosed as gastric cancer metastasizing to the adrenal gland. The patient was referred to our hospital for close examination and treatment and admitted. After his informed consent had been obtained, the patient received one course (4-week administration and 2-week withdrawal) of S-1 at 50 mg/body x 2/day. Abdominal computed tomography performed after the end of the one course revealed that the tumor had become undetectable. This condition was still maintained at the end of two courses and judged to be complete response (CR) (in accordance with the WHO Efficacy Judgment Criteria). CR has continued to be maintained to the present time, even after seven courses. There has been no previous report of S-1 showing remarkable effectiveness in a patient with 5-FU-resistant gastric cancer metastasizing to the adrenal gland. We consider that the efficacy of S-1 for treatment of 5-FU-resistant gastric cancer should be verified.