Primary small intestinal cancer is very rare. We experienced 4 cases from 2001 to 2013. Case 1: A 46-year-old man presented with abdominal pain and melena. Computed tomography (CT) revealed a tumor in the jejunum. We performed partial resection and lymph node dissection. The histological examination confirmed the diagnosis of moderately differentiated adenocarcinoma, SEN0H0P0M0. He has been recurrence-free for 13 years. Case 2: An 84-year-old woman presented with abdominal pain and vomiting. Gastroscopy showed a tumor in the upper jejunum, and she was diagnosed with adenocarcinoma. Postoperative diagnosis was SEN0H0P0M0. She has been alive for 7 years. Case 3: A 66-year-old woman presented with epigastric discomfort and back pain. Examinations confirmed poorly differentiated small intestinal adenocarcinoma with multiple liver and lymph node metastases. She refused chemotherapy and died 1 month later. Case 4: A 60-year-old man presented with abdominal pain and vomiting. CT revealed a tumor in the jejunum. Gastroscopic biopsy led to a diagnosis of poorly differentiated adenocarcinoma. We performed partial resection but there was extensive lymph node metastasis and peritoneal dissemination (cSIN2H0P3M1) so curative resection was impossible. Two courses of chemotherapy with S-1 and CDDP were administered. However, chemotherapy was not effective. He died 3.5 months after the first operation. Based on 2 of our cases, the prognosis for primary small intestine adenocarcinoma with lymph node metastasis or peritoneal dissemination was poor, with survival of less than 6 months. However, N0 cases without peritoneal dissemination can achieve long-term survival with curative resection. We report these cases with a review of previously reported cases in the literature.