This single-institution experience retrospectively reviewed the outcomes in 21 patients with primary duodenal adenocarcinoma. Twelve patients underwent curative surgery, and 9 patients underwent palliative surgery at the Chiba University Hospital. The maximum follow-up period was 8650 days. All pathologic specimens from endoscopic biopsy and surgical specimens were reviewed and categorized. Twelve (57.1%) patients underwent curative surgery (R0): 4 pancreaticoduodenectomies (PD), 4 pylorus-preserving PDs (PpPD), 2 local resections of the duodenum and 2 endoscopic mucosal resections (EMR). Palliative surgery was performed for 9 patients (42.9%) following gastro-intestinal bypass. The median cause-specific survival times were 1784 days (range 160-8650 days) in the curative surgery group and 261 days (range 27-857 days) in the palliative surgery group (P = 0.0003, log-rank test). The resectability of primary duodenal adenocarcinoma was associated with a smaller tumor size, a lower degree of tumor depth invasiveness, and less spread to the lymph nodes and distant organs.