A 7-years-old, 3,5 kg Birman cat was evaluated because of a history of anorexia, regurgitation, vomiting, and lack of weight gain. Radiographic and ultrasonographic examination included a gastric wall thickening, thickened pylorus without normal pylorogastric serosal continuity and stenotic pyloric outflow orifice. Diffuse infiltration of the stomach wall with thickening at the level of greater curvature and pyloric antrum was observed during exploratory laparotomy. A gastrectomy of the greater curvature of the stomach with end-to-end gastroduodenostomy (Billroth I procedure) was successfully performed. Four weeks after surgery, the cat was eating and drinking normally. Occasional vomiting one week after surgery was managed medically. Four weeks after surgery, the owner reported that the cat seemed normal in appearance and behavior, but she declined the chemotherapy plan proposed. A gastric neoplasia was suspected at the time of surgery and postoperative histologic examination of the excised tissue revealed a gastric lymphoma. The cat of this report was treated successfully with a Billroth I procedure.