Gastrointestinal stromal tumors are currently the object of a great clinical and experimental interest. We are presenting the case of a 69-year-old patient, who was presented with lower gastrointestinal bleeding and dyspeptic symptoms over the last six months. The colonoscopy showed a large tumor of the sigmoid and the gastroscopy a large gastric tumor of the antrum, which were histologically diagnosed as colonic adenocarcinoma and gastric stromal tumor respectively. The patient underwent a sigmoidectomy and a partial gastrectomy. Six months after surgery were the clinical condition, abdominal CT, gastroscopy and colonoscopy without pathological findings. To our best knowledge, this is the second report of a synchronous gastric stromal tumor and a colonic adenocarcinoma in medical literature.