Primary adenocarcinoma of the duodenum is an extremely rare disease, and represents only 0.35 per cents of all gastrointestinal malignancies. Early detection of the disease is difficult because doesn't have pathognomonic simptoms. The Whipple procedure is the optimal method of treatment. The authors relate one case of a adenocarcinoma of the duodenum in a 65-year-old white female with a history of abdominal pain for a six-month period, associated with postprandial fullness, vomiting and weight loss. Endoscopy showed a elevated tumor in the second part of the duodenum, with partial obstruction of the lumen. Histological study of endoscopic biopsies reveled a moderate differentiated adenocarcinoma of the duodenum. The treatment was surgical. The authors comment on the more important aspects of this pathology