The histories of 27 patients who had primary duodenal malignant lesions are reviewed. There were 16 women and 11 men with an average age of 60 years. The incidence of primary small-bowel malignancy in routine autopsies is low; however, the absolute involvement of the duodenum is high. The majority of the lesions were adenocarcinomas; leiomyosarcoma was the second most common histologic type. In this series the highest incidence of primary duodenal tumors was in the infra-ampullary part of the duodenum. The symptoms of primary malignant lesions in the duodenum are nonspecific but referable to the gastrointestinal system. The differential diagnosis should include consideration of pancreatic carcinoma, ampullary carcinoma, and several other neoplastic, inflammatory, and metabolic conditions. Roentgenographic diagnostic accuracy can be high if a high index of suspicion is maintained. The upper gastrointestinal series, hypotonic duodenography, cineradiography, and celiac and superior mesenteric angiography should be used. The 5 year survival rate is 27 per cent in this series.