ABSTRACT. Araujo D.C.C., dos Santos I.O.V., da Silva M.A., Pessoa C.C. da V., de Carvalho J.R.G., Lopes N.L. & Fernandes J.I. [Gastrointestinal Sarcoma in a Dog – Case Report.] Saroma Gastrointestinal em Cão – Relato de Caso. Revista Brasileira de Medicina Veterinária, 38(supl. 3):31-38, 2016. Programa de Pós-Graduação em Ciências Veterinárias, Anexo 1, Instituto de Veterinária, Universidade Federal Rural do Rio de Janeiro, BR 465 Km 7, Campus Seropédica, RJ 23897-000, Brasil. E-mail: firstname.lastname@example.org Gastric cancers in dogs are rare and represent less than 1% of all malignancies in this species. There is a higher incidence in male dogs, large, with an average age of eight years. The etiology is not well defined, but studies show a relationship with gastric infection by bacteria of the genus Helicobacter sp. The diagnosis is based on history, clinical signs such as vomiting, regurgitation and weight loss, ultrasound, endoscopy, histopathology and immunohistochemistry. The choice of therapy is surgery, performing the excision of the tumor with wide margins. Adjuvant chemotherapy does not work properly, except in cases of gastrointestinal lymphoma. The objective of this study was to report the occurrence of gastric cancer in a dog, male, tenyear-old German Shepherd that had as main complaint regurgitation and vomiting with evolution of a month. Surgery was performed and histopathological diagnosis of gastrointestinal stromal tumor (GIST). Subsequent immunohistochemical examination revealed fibrosarcoma. After surgical resection and adjuvant chemotherapy animal survival was eight months after diagnosis.