We describe a case of gastric metastases from a lobular carcinoma of the breast in a 73-year-old woman who had undergone a left mastectomy with axillary dissection 15 years earlier. The initial diagnosis was diffuse-type gastric carcinoma as evaluated both by analysis of gastric biopsy findings and ultrasonographic endoscopy. The definitive diagnosis of metastatic breast cancer was confirmed after subtotal gastrectomy for a presumed primary gastric carcinoma and was obtained using a panel of specific immunohistochemical markers. The distinction between primary and secondary gastric malignancies in patients with a history of lobular breast carcinoma may not be merely an academy exercise, since the treatment and prognosis of the two situations are different.