Primary small-cell carcinomas of the stomach are rare and aggressive malignancies with poor survival rates. Preoperative diagnosis is difficult and a standard treatment is not yet established. We have recently experienced two cases of a primary small-cell carcinoma of the stomach. The first case was a 65-year-old man with epigastric soreness. Endoscopic biopsy showed an adenocarcinoma. He underwent a radical subtotal gastrectomy with D2 lymph-node dissection. Pathology revealed a collision tumor of a small- cell carcinoma and an adenocarcinoma with submucosal invasion and with metastasis in 20 out of 48 lymph nodes (T1N3M0). The second case was a 64-year-old man with epigastric soreness. Endoscopic biopsy revealed a small-cell carcinoma. There was no evidence of a primary tumor in the lung. A radical subtotal gastrectomy with D2 lymph-node dissection was performed. Pathology showed a pure small- cell carcinoma with proper muscle invasion and with metastasis in 1 out of 36 lymph nodes (T2aN1M0).