Intravascular lymphoma (IVL) is a rare, high-grade, extranodal lymphoma characterized by selective proliferation of neoplastic lymphocytes within the lumen of small vessels. A 10 yr old female intact mixed-breed dog was presented with a 7 mo history of vomiting and anorexia. Physical examination revealed abdominal discomfort. Ultrasonography and endoscopy identified a submucosal gastric mass. Excision was performed by partial gastrectomy and histopathology and immunohistochemistry confirmed a T-cell IVL. The owner declined chemotherapy, and the dog was instead treated palliatively with prednisolone. Two months after surgery, vomiting recurred and abdominal ultrasonography revealed a large gastric ulcer with focal peritonitis. The dog was euthanized 4 mo after initial presentation and postmortem examination confirmed IVL recurrence in the stomach and an isolated nodule of neoplastic cells in the omentum. No involvement of other organs was found following histopathological examination. This is the first description of primary gastric intravascular lymphoma causing chronic vomiting in a dog.