Gastrointestinal stromal tumors (GISTs) constitute the most common primary mesenchymal tumors of the digestive tract and characteristically express c-kit (CD117). GISTs are the most common non-epithelial tumor of the GI tract and frequently originate from the stomach and small bowel. Specifically, the synchronous occurrence of a GIST with other epithelial tumors is rarely reported. Recently, we discovered one case of a concurrent gastric cancer and a small bowel GIST that was initially suspected to be peritoneal seeding from gastric cancer. The patient was initially admitted with epigastric pain. Gastric cancer with peritoneal seeding was suspected after an evaluation. Following a laparoscopic examination, a distal gastrectomy with D2 lymph node dissection and small-intestine segmental resection was performed. The final pathologic diagnosis was early gastric cancer and high-risk small bowel GIST. The patient refused adjuvant therapy for the GIST, and currently shows no other marked indisposition. He has been disease-free for 14 months.