BACKGROUND Metastasis to the stomach can be found as the first presentation of breast cancer, although it is very rare. The authors report an unusual case of metastasis to the stomach as the first presentation of breast cancer, which had a good prognosis. CASE REPORT A 51-year-old female underwent radical subtotal gastrectomy and chemotherapy because of gastric cancer with distant metastasis. At the time of diagnosis of gastric cancer, she had a negative result from routine mammography. One year later, a newly detected lesion on routine mammography was confirmed as breast cancer. Initial diagnosis of gastric cancer was changed to metastatic carcinoma from breast cancer through immunohistochemistry after bilateral mastectomy. After the completion of chemotherapy, she is currently receiving treatment with letrozole, without recurrence for 66 months. CONCLUSIONS Considering metastasis from breast cancer might be needed when unusual presentation of gastric cancer is observed even though gastric cancer is still one of the most common malignancies in Korea. Immunohistochemical analysis is helpful for diagnosis. Surgery for metastatic carcinoma of the stomach could be another option for treatment.