The authors describe a fatal case of gastric perforation secondary to an ulcerated metastasis in a woman with undiagnosed breast cancer. The 48-year-old woman, with no significant medical history, presented with weight loss, persistent dyspepsia and pain in the epigastric and mesogastric region. She was treated by her primary care physician with proton-pump inhibitors and antispasmodics. The following day she was found dead at her home. External examination showed a tumefaction in the lateral region of her left breast, near the axilla. Autopsy revealed 1000 ml of turbid, light-brown peritoneal fluid in the abdominal cavity and a perforated gastric wall. Histological examination of the breast mass showed an infiltrating, poorly-differentiated breast carcinoma. Microscopical analysis of the stomach wall revealed a perforated metastatic gastric ulcer. Immunohistochemistry was required to confirm the neoplastic involvement of the stomach due to metastatic breast cancer.